"– I mentioned that some humans can do it?"

"By clicking their tongues, usually, or just otherwise repeating the same noise at regular intervals."

"Right. But I didn't think clicking your tongue was a high pitch."

"I don't know, maybe not, but it is at least more periodic in general they footsteps I think."

"More periodic meaning – more regular, or done more often, or…?"

"I mean I'm pretty sure it's made so that there's an actual period."

"Oscillation period, you mean? Yeah, I think they do it at a sort of, uh, regular interval. I'm not sure, though."

"Yeah, anyway, still impressive."

"Yeah," agrees Matt. "So– are you just listening for how long it takes, or…?"

"Nnnnot really?" he says. "It's just echoing and I can sort of go 'oh right it came from over there'." He points at a wall to the left of them. "And I can visualize how far that is."

"That is really cool and not how echolocation works at all I think?"

"You mean, in the humans who apparently do it or normally in other animals that are actually, like, optimized for it or whatever?"

"Both?"

"I have no idea," he says. "How do you think it works, though, like– I didn't actually research this."

"I didn't, either, I just have vague memories of having read, but I think the relevant thing is how long the same sound takes to reach you when repeated, rather than just once?"

"Okay, right, but they're footsteps, plural, and so I'm not just relying on one? I guess the distance changes…"

"I think it's more about tridimensionality, a single pulse can give you distance, multiple ones can give you shape."

"Right, so." Pause. "The confusion is, what, about whether my footsteps give me tridimensionality of the wall?"

"Well no just that the way you described it didn't sound like you were doing that but if you are I stand corrected."

"I'm not consciously processing where all my footstep echoes are going and coming from and building a 3D model of the world around me, no, but I sort of– know where things are anyway?"

"Weird."

"Do you know what they are, too? Presumably, I guess, you're not hitting any walls or anything."

"– I know there's a solid barrier about however tall over in a particular direction, and I know that the ground I'm walking on continues to be sidewalk and not, like, grass or road. So yeah. But not anywhere near as well as if I had my eyes open."

"Can you see street signs and stuff?"

"I can tell there are poles into which I should presumably not walk, yeah. If you mean ones attached to the side of buildings or something, uh, maybe but I don't think there are any around right now?"