yeah they use some chemical juices to digest the food. It takes a while depend on the size of the insect.
I saw the one that it eats the frog but I think in those cases that trap dies because It is to big to digest or something like that!
I watched a program on them and they have little "trigger" hairs inside the part that closes. They showed a close up of a fly walking and it had to hit 3 hairs before the trap would close. Deffinatly a cool plant.
I remember when I was a little kid around 8 years old always wanting to have a Venus Fly Trap because it could eat bugs and I thought that was cool, but after seeing a few videos,"this is freaking amazing" what they do.