The smallest BCI I can think of is the peruvian boa. My bosses is short(5-6feet) full grown but very girthy, very strong. Not a slender snake, makes 5 feet look huge! I mean a 5 foot ball python versus a 5 foot boa is a big difference. This guy must weigh close to 10-15 pounds, you might think it's nothing, but it's surprising. Good luck, hope this helps! ~Caylan.S.~