It ends up being a hand that is written on, the back to be specific and he's glad there's some dashes in the numbers because he's read that you could start communication on your own skin and that's creepy. He'll transfer it to his phone when he gets back to the school, if he'd had it with him he could have just put it in now but of course- it's back in his dorm on his desk.

"You're sure? I mean it- I don't want to find out you slipped into a coma or something just after I left." Talk about guilt if that happened. "I'll contact you when I get back to my dorm- just let me know you didn't die okay?" He's probably being over dramatic, but this has been a very weird day and the kid still has some gum in his hair.

Also the fact he might know him from this 'past life' bullshit? Doubly worried about him disappearing.