The snake one is on snopes... as FALSE.
http://www.snopes.com/critters/snakes/measured.asp
One of Hypo's Biology teachers told us a story, in a very matter of fact manner, at open house, about the boa constrictor she took home to take care of over winter break. It got out and was living somewhere in her house. She knew it was still alive because she'd find the skin it shed from time to time and she suspected it was in the wall by the shower pipes because the shed skin was always in the basement under those pipes. She said it really freaked her husband out that it was in the house somewhere, but she wasn't concerned. She assumed it would show itself because it was getting close to the year mark since it had eaten and she said it only had to eat once a year. I never did hear whether she found it.