Exploding Cantaloupe

OK... Perhaps "exploding" is too strong a word here, but I'll describe the incident, and you let me know.

I bought a cantaloupe from our local Giant grocery store last weekend -- I've been meaning to post this for a while, but just haven't.

I didn't get to cutting up the cantaloupe as I had planned, so when I went to bed that night, I just left it sitting on the counter -- it's not refrigerated at the grocery store, so why should I have to refrigerate it at home?

Well, when I came down the next morning, small cracks had formed on the cantaloupe and the cantaloupe juice had leaked out. However, the most disconcerting thing was that the top of the cantaloupe was covered in some type of foam substance.

Anybody ever hear of this type of thing?