Swallow and bombs away! He's considerate enough to drop it on the otherside, hell if someone he knew and didn't like was there, he might have thrown the cup at them. He's got a slightly confused look on his face and points out the marks on Bob's skin.

"The hell's your problem? You're hanyou aren't you?"

...ahh, now it kicks in, well, two things anyways.

"Hanyou, y'know, half demon."

Inuyasha's thinking that this guy's either ignorant of his heiritage or he's in denial. Of course, the mun knows better but, is willing to let her pup make an ass of himself. It's in-character for this one after all.