He is taken aback. Obviously this is not an old friend, or even someone from his own time. The fangs are definitely menacing, though, and Sun Wukong takes it like a challenge.

He shifts from the human face to his own and bares his own teeth. "'No' isn't an answer," he says. Most interactions requiring etiquette head steadily downwards for Sun Wukong, and this one seems to be descending at a startling speed. "I'm a foreigner too, we're alike that way." He switches to his native Chinese, though that probably wouldn't help.

Eh, if they can't communicate well they can't communicate well. Sun Wukong finds this probably-not-demon-some-kind-of-entity-he-can't-understand interesting enough to pester him further.