How would you know if it's gravel or grate or cement? How would the foot know?

I work with the artists to delineate every single panel on the ground in the game, every way you can walk. In fact, even surfaces that you can bump into have the kind of surface type written down, so that if you accidentally walk into the wall, it'll make the right kind of sound.

Again, more immersion, right? And then probably we'll have the guy going "ow" or something like that, so that's even more sounds.

Yeah, that would come up from his head area, not from the ground.