I experienced similar problems with my own burm a couple years ago. I had the cage a couple degrees too cold on the cold side. If its not at least 80 cold side, 90 warm side, the snake might not eat because of that. My temps are now 82 cool side and 92 warm side, and he has yet to refuse a meal since upping the temps(almost a year ago now). Also, for prey size, definately go bigger! They can fit amazingly big rodents in their stomaches for their size! Good luck, ~Caylan.S.~