[He's at least paying attention to how Ayumu's acting here so he does catch that pause, even if he can't necessarily tell why it happened. But either way, he's got enough to go off on.]

If this was the only place it happened, sure. That doesn't explain why you were showing a couple of the same signs a couple weeks back.

[It's not a particularly accusatory statement the way he's saying it; more just like a statement of fact than anything else. Mahiro's just interested to see if Ayumu would try to keep dodging it anyways.]