Trees, Grass, and Dust

A conversation had this morning:

John: I got some new bandages.

Marly: That's nice. Why did you get the latex-free kind?

John: I'm allergic to latex.

Marly: No, you're not.

John: Really? What am I allergic to?

Marly: Penicillin.

John: Oh.

He's not allergic to penicillin either. ;)