Jacob would like to say that he didn't show any surprise, that he played it cool, because he's just so experienced at dealing with the impossible and it's no big deal, but that'd be a lie. His eyes are wide and his mouth drops open a little.

"Uh, hello."

Shock aside, introductions should be in order.

"Yeah. I'm uh...I'm Jacob Stone. What's your name?"

To be fair, it wouldn't be the first time he'd been abducted by vines, so he could claim that as to his reaction, and for a split second he's ready to run, but he stands his ground. He was honestly expecting something like a forest spirit or a grove of sentient, whispering trees.