I'm not sure if this is the norm but I fast my snakes every couple of months. What I've noticed from my own observations in my small collection is that every once in awhile my snakes get finicky about eating and start refusing a bit. I won't feed for 2-3weeks and then after that they pickup the pace and they're all eating fine again. I only do this 2-4 times a year. I'm not sure if that sounds normal or if anyone else does it but it works well for me.