Quote Originally Posted by Litmaster View Post
I think the answer is simple: Chuck just got through stabbing a bunch of Zeds with that spear, then used the same blood-soaked spear tip to stab Mark.

Boom, instant infection.
I thought that too at first, but I'm pretty sure Chuck didn't use the spear before that. The one sombie that they kill before entering the room to grab the phone wasn't killed with a stab, but more of a smack from something, so I'm thinking Jeremy...It also sounds like he confirms the kill afterwards, so...