I've had rat snakes do this...one especially that remembered the belt loops on my jeans & made a beeline for them when I picked her up...I guess she liked the feeling
of secure "toe-holds"? My Florida/yellow rat snakes are too big for belt loops, but it's not hard to get them to just snug themselves around my waist. (the males are
about 7' long, so they can do this easily with length to spare)