boo-boo's and boogers

Tonight after Josh went to bed, he came back down the stairs in tears.  This conversation ensued:

Y: Josh, what's wrong?
J (sobbing): Mommy, if you eat your boo-boo's, is that what makes chicken pox?
Y: No, Josh, eating your boo-boo's does not cause chicken pox. (pause) But you shouldn't eat your boo-boo's.  Do you know what that is?
J: No.
Y: Your boo-boo's are dried blood, so you shouldn't eat them.
J: It was an accident.  My favourite is boogers but sometimes I eat boo-boo's by accident.
Y: Well, you shouldn't eat boogers OR boo-boo's.
J: But Mommy, sometimes I eat boogers and boo-boo's by accident and sometimes I eat them by purpose.

The reference to chicken pox is a remnant from a past conversation where Josh started asking me how we get chicken pox (no idea where he heard about it from!).  I tried explaining the virus thing, but apparently the concept didn't sink in.