"I wouldn't have known." As far as Asriel's concerned, the really cruel thing to do would've been to dangle it in front of him and then yank it away. That's probably what he would've done. With a lot more yelling to get the humans' attention, no doubt.

He turns his arms over, flexing his fingers, as if trying to see the shield again. But it's totally gone! That's kinda cool.

"But yeah, thanks! That's really neat."