Any reflecting surface would have the reflecting
pulses match in time. The reflection would be
third order, very small, but the time sequences
would match, making this an important video presentation.
That makes sense as long as the possible reflective surface was stationary, and whatever possible reflective surface if stationary, was not being subjected to a shutter-like effect -- like a person standing in front of it, but them moving away, followed by the surface being blocked again from direct sound either coming, or going.
I'm just trying to eliminate possibilities.