What's black and slimy?

So this morning I was waking up slowly and all of a sudden, I saw something strange at my feet. Lying flat on the ground was a two inch black frog. Cursory examination revealed that the frog was dead. The most mysterious part was that my room was sealed. The windows were closed tightly and I even put a pair of trousers at the base of my door so mosquitoes couldn't fly in that way. Yet somehow, this not-very-tiny frog found its way in and decided to sprawl out dead at my feet. Well, if they were more effective at catching mosquitoes, I'd keep a few of them on patrol every night.