Interesting. Leareth looks around, and throws the pen he's been writing with at Bruce. It bounces off. 

He starts to prepare a levinbolt and then stops; this seems like a bad idea to try without asking. "Does it block magical attacks as well? Also, is there a force limit to the physical protection – if the ceiling collapsed on you, for example, would it protect against that or fail?" 

"It does block magic attacks--or at least it blocked Larry's magic missile--but it definitely wouldn't hold up to the ceiling collapsing." It's good that that ill-advised experiment with the cinderblocks and the third story window ended up being useful for something.

"There is probably a power limit for magical attacks as well, then," Leareth says. "Hmm. I am not sure how to safely test it. Can you shield something other than yourself? I could also test with a very weak levinbolt, that will not harm you if it penetrates, but that will not give us an upper limit and it would be valuable to know." 

"I don't know how to shield something else, sorry." He really wants to suggest that they can find an upper limit by just working up gradually, but he's pretty sure the shield goes from "works" to "doesn't" with no partial-failure stage in between and frankly he's too scared. "I know the upper limit is somewhere below 'a bunch of cinderblocks pushed out a third story window.'"

"...That sounds like a risky experiment? Was anybody hurt?" Well, clearly Bruce is fine now, it can't have been too disastrous. Leareth frowns. "Shield me," he mutters to himself. "The incantation does specify that the target to be shielded is yourself. Can you... What is the mental component? If you were to say, Shield that, and hold the target in mind...?" He's not sure if that will make it even less efficient but it seems worth trying. 

Bruce declines to answer that question, because the truth answer of "I had a concussion but Larry did a really good job of lying to my parents about how I got it" is desperately embarrassing.  "Shield thett, er, shield that? Does that translate to just "make a shield" or something? I can give it a shot." He checks the nearest box for stuff that won't be missed if they destroy it and comes up with a basketball. "Shield that."

Bruce can't tell if a spell does anything except by seeing the effects; he aims a kick at the basketball and gets deflected. Leareth can see that it's still massively inefficient but not more than the previous version.

Leareth throws a weak levinbolt at the basketball; it's also deflected. He tries progressively stronger attacks until, at around the point that a strike would generally be powerful enough to get through a Master-potential mage's ordinary shields, the magic shatters – backlashing at him a little, but he's ready for it this time – and the ball goes flying at the wall, bouncing and landing with visible scorch-marks.

"Interesting," he says quietly. "I wonder if different incantations... Can you try Build a shield here?" It's longer, less speed-optimized, and he's not sure if changing it around will interfere with the power requirements and thus the accompanying gesture, but worth checking.  

He can totally try that! The first time, he screws up the pronunciation and nothing happens. The second time, he gets it right and it works about like the previous shield, except it ends up attached to the area of floor rather than the basketball. This doesn't matter much because the basketball isn't going to move out of the area under its own power, but it is a visible difference to Leareth's Sight.

Leareth makes a note. "Similar," he says, "but specified to a location rather than an object, worth keeping in mind." Unfortunately it doesn't look like it's any more efficient. "I wonder... If you use the gesture for Fly, but that incantation, I am curious to see what will happen. If there are simply side effects from power leakage, I can take care of them." He smiles briefly. "I doubt I would mind the snack." 

"Sure, here goes."

(Having Leareth around makes doing magic science so much safer and easier, and he has good experiment ideas, and in general it's just so good to have an adult around who knows what he's doing.)

This time, half the extra power goes into the shield, and it stays up for about fifteen seconds, and the rest goes into heat and tries to set Bruce's sock on fire.

Leareth snatches up the free magic before it can do more than spark a little. "Hmm." He glances at his notes, trying to remember the order of spell-gestures against his guess at the power being drawn. "Perhaps try with the gesture for Alter Self now?" 

Gesture! Spell-casting! This produces somewhat less runaway edible magic and makes the shield last about ten seconds.

Well, that's somewhat irritating. 

"I will consider this further," Leareth says. "It looks as though we cannot manage to direct all of the excess into the shield. In the meantime, I suppose you could demonstrate Darkvision – I think that is the only one we have not yet run through." 

"Sure. It's convenient that we're already in a basement." And he can turn out the lights and tell Leareth how many fingers he's holding up from across the room, when Leareth can barely see his own hand in front of his face at all.

Also very useful – particularly for spies. Bruce doesn't have any combat spells, exactly, but a number of them show promise for subterfuge. 

He consults his list. "Is that everything, or are there more that we forgot to cover? On my end, I have not showed you much combat magic, but it is...not clearly safe to practice inside. Also, there are compulsions, but I could only demonstrate that on you and I would understand if you are not comfortable with it." 

"Let me think about it for a minute," he says, staring at his shoes. On the one hand, compulsion magic sounds scary. On the other hand, it's quite clear by now that if Leareth meant him harm he would have done it already; it's not like Bruce could stop him. And his brain is oh-so-helpfully generating examples of ways it could be useful to be able to control one's allies in combat. And, no sense not admitting it to himself, he's curious how it works and what it would feel like.

"I think I would be okay with trying a compulsion, if it definitely wouldn't do anything that wasn't temporary. Can you explain how it works, first? Like, does it make you want to do things or just do them, can you make someone do something you know how to do but they don't, stuff like that?"

Leareth frowns, trying to figure out the appropriate order. 

"On the question of shifting wants versus actions, it is not that simple; however, it is certainly much quicker and easier to cast a compulsion that forces actions rather than changing all of the underlying motives, and so one would almost never use the latter in practice." He smiles thinly. "The latter would be impossible to do subtly, since it would take days or weeks to lay all of the sub-components that would cause someone to feel internally motivated to, say, assassinate a certain target. Since this would be very noticeable to the victim, it is unclear what the point would be." 

He pauses, clarifying his thoughts. "It is also possible to use a compulsion for something that the caster knows how to do and they cannot, however, again it is something that one must work for, since in practice what one is doing is building in all of the component mental motions that would usually go into the skill. This method can be perfected once and then repeated many times, though, which offers efficiency gains. I have implemented it in military contexts, voluntarily, to speed training for soldiers learning certain fighting techniques and particularly those which require coordinated group formations." 

"As to your first question – I can very easily place a compulsion temporarily and then remove it without leaving any traces. Assuming that you trust me to do so." Another thin smile. "You could also check for yourself with Detect Magic – an active compulsion is detectable by mage-sight in my world, so I assume that your spell would also work." 

Using it for faster training sounds unfairly awesome in a The Matrix "I know Kung Fu" way. "I trust you to take it off, but you still haven't told me enough examples of simple ones for me not to be confused."

Leareth nods. “A simple example would be a basic action - we might say, going to that box of clothing and removing a shirt and bringing it to me. Usually it would be tied to a trigger phrase rather than initiated by the casting, and would be invisible to the subject in the interim. A skillful mage can cast one subtly enough that the subject does not distinguish it from their own thoughts; for example, if we were not already having this conversation, I could compel you to go upstairs and obtain food for us without your necessarily remarking it was not your idea; but that is not really the purpose of this demonstration, so I would not try to be sneaky about it.”

"Okay, that" is terrifying "makes sense. I'd be okay with trying it now." before I lose my nerve.

“If you are sure.” Leareth looks hard into his eyes for a long moment. “I am casting it now,” this will not feel like anything or be in any way noticeable to Bruce except that Leareth looks very focused for about ten seconds. 

”I would like a shirt,” Leareth says, conversationally, and now Bruce is going to find his legs moving of their own accord, over to the corner of the room where the box is, and his hands opening it and reaching in...

It's not at all an unpleasant or disturbing experience. In fact it's exactly like being lost in thought and getting up from his desk and getting a soda out of the fridge and being back at his desk before consciously noticing he's thirsty. But the fact that this is something magic can do, to people in general and to him in particular, means he can't just let himself do things and trust that his body is generally going to work in his own interests. And he also can't pay constant conscious attention to his every physical action at all times while also functioning as a human being, so. Once the compulsion stops moving him around, he spends a long moment very still, except for a racing heart.

You need to calm down, he tells himself. This isn't any different from the situation you were in five minutes ago, you're just more aware of it. It also isn't any different from being in a universe with an omnipotent God. Your free will has always been contingent on other beings choosing not to mess with it, and you've made it sixteen years that way, so stop breathing manually and go back to doing science.

"Huh."

"I can see why you would use that for teaching things, I bet it would be way easier to learn to throw a football or whatever if you could watch yourself do it first."

(He's still breathing manually, embarrassingly enough. He'll stop eventually.)

Leareth is one hundred percent not fooled. He’s slightly tempted to read Bruce’s thoughts to figure out what’s going on, but he doesn’t.

“Bruce,” he says. “Bruce. Look at me.” He waits. “You seem...not all right. Listen to me; I swear to you by every star in the sky that I will not do this to you again without your permission. Now. Can you tell me what is troubling you?” It shouldn’t have been an especially distressing compulsion.

"I'm sorry. It's not, I'm not worried about you doing it, I said I trusted you and I meant it and you did get permission. It's just, knowing that's the sort of thing that can happen. That it could have happened before and I would never have known about it. I know it doesn't make any sense to freak out."

"I know." Leareth spends a long time searching for the right words. "You live in a world where your mind is not inviolate," he says finally. "This is a true fact about reality, and one that is justifiably painful. I grew up knowing that compulsions existed," this isn't technically a lie even though he doesn't remember growing up the first time, he's pretty sure he knew about the concept, "and that once I was trained as a mage, I would have defences. You are learning of it only now – in fact, your world as far as I know does not have this particular magic. It makes sense for this to be an unpleasant shock and realization, even if nothing about reality has truly changed."

He pauses, thinking. "I can put my own shields on you if you wish," he says. "Such that nobody else would be able to meddle with your mind. It would be advantageous to me – I do not wish my allies to be vulnerable. The downside is that it would be visible to Detect Magic; I am not sure if you expect this to present a problem?"