@Lao lee, I get it ;) when I ask about this, I always get one of these answers:
2) joint hypermobility, hyperlaxity.
3) sessions of painful strechings, pain pain !!! (this one the most of the time XD)
btw, which martial art did/do you practise?
It will make your life short, seriously~~what the purpose of doing that kind of stuff? making youself curve like snakes??~~