A squeeze ensures they don't let go, and then they progress into petting it. Just to feel how soft it is, mind you, they're not trying to be nice for no reason.

Frisk hmms and glances meaningfully behind themselves. Of course they didn't, there's nothing on them to grab. If he wants anything, he can pick them up by their shirt or pet their hair, though the latter will get plenty of just-trimmed ones tangled in what they have now all over his hands. If it's not all over him already just for being near them at all.