He was feeling... less worried about this guy, or at least less like it might be his responsibility to make sure this person is Well, up until he got to unsterilized needle.

Ed's spent a lot of time in and around doctors, automail mechanics, and hospitals. It's not his specialty, but he knows some basics. You don't use un-sterilized equipment. That's how people get diseases and die.

"Hey, I think maybe we should get you to a hospital. That doesn't sound safe."