"Oh?"

"The, uh, mental state I mentioned, is... belief. Kinda. Expectation, really. I have to expect a thing to happen, and it will. But the trick to it is that other people's beliefs also count. If I tell you I can conjure a thing, and you actually expect me to be able to, it's much easier for me to do it."

Oh. 

... Oh. 

Mary immediately expects a rainbow ping-pong ball to appear outside her space as hard as she can. 

Nothing happens.

Hmm.

"I'm going to conjure a ping-pong ball right over there." She points to a spot outside her range.

Then she forces the ping-pong ball. 

There it is!

"That wasn't me conjuring right then -- that was you. The ping pong ball was outside my range.

I really think conjuring Heidi a body would work."

"Then let's try it again."

They do!

This time Mary forces Heidi instead of relying on Sadde to do it himself. 

There she is.

Can Heidi move her arm? 

Yep!

"Cool!"

Heidi grins. 

Can she touch her nose?

With absolutely no sensory feedback, but yes she can.

"I just tested proprioception by touching my nose and couldn't feel my nose." And realized that she may be supplementing her proprioception with Mary's secondhand sight. 

"Mary?" She asks. "Could you turn around?"

Heidi, that's not how it works, if you make a falsifiable test and then expect the test to fail it's going to fail, he just told us his power works like forcing. 

 I was going to suggest that you try forcing me through a non-visual sense. This is a physical, corporeal body. I will not disappear when you are not looking, so you won't have to visualize me. 

I'm just scared that if I try to hard to not perceive you you'll disappear, or --

No. No. You're real, this is what we're proving, right now, that you're real even when I'm not looking.

Yes.

... Mary turns around so that her back is to Heidi. She focuses on the air, on the feeling of someone reading over her shoulder, of the tension of waiting for someone to sneak up behind her. She tries something she's rarely ever done, forcing smell, and Heidi smells of lavender and cinnamon toothpaste. 

"Sorry about that," Mary says for Sadde's benefit. "We were arguing about tests."

Can Heidi lift her arm?

Sadde watches in curiosity and shrugs. "It's alright."

And yes, Heidi can in fact lift her arm. She can still not, however, get any sensory feedback other than anything Mary believes she can.

Heidi starts to dance! The movements are slow and jerky and become progressively less so as she does more of it. 

"So, how do you conduct tests for your power? I wouldn't think you could do science to it properly if it's so dependent on expectations."

He giggles.

"It's quantitatively dependent on expectations, and stuff like passive, active, or vague ones from various people contribute differently to it. There's also a few limits related to how much attention I can pay and how many things I can keep track of—even subconsciously. Also one of my girlfriend's powers is being categorically immune to mind powers so her expectations completely fail to affect what I can or can't do."

"That sounds inconvenient."