He can tell from one look that Mick's a hardass: it's written in his body language and his worn face, like he's Seen Some Serious Shit. Peter already likes that about him.

"Enough. If it helps, I won't go screaming for the hills at the first zombie," Peter doesn't let the hard stare slow him down. "Screaming would just drag its buddies to our position."

The old Peter Quill might've been tempted to abandon Mick, though, if things went too far south. Now that he's a Guardian and he's all respectable, he has to content himself with the idea that he'll drag Mick to safety if he has to and if neither of them is bit. A zombie gets too friendly with either one, even a graze, and there's no point in stumbling back to camp. Sucks, but it is what it is.