These are one of the oddest monsters under the bed from my childhood. I don't recall exactly where I got the idea, but I do know it didn't just spring into my head unbidden - I heard it from a friend first. These horrid little things would wait around the base of the bed for you to let a hand dangle over, then they'd chew off your fingers. I remember being incredibly afraid of this, even though I didn't fully realize at the time just how heinous that would really be. Of course, there was a defense: frog heads were terrified of cats. Toy kitties would keep them at bay, and real ones could possibly banish frog heads from a house altogether. It's because of that (and the fact that I just like cats) that I begged my parents to get me a pet kitty when I was young. Of course, since my dad is allergic to them, this never happened.
By the time I was 8 or 9, I realized that they didn't exist - or at least didn't want to eat my fingers anymore, but they returned to terrorize my little brother. Eventually, though, he saw the Neverending Story, and decided that Falkor, the luck dragon had the power to banish all frog heads into The Nothing, where they'd be forever destroyed. From that day forward, the frog heads never terrorized him again, either.