bull snake not eating

[reptocarl]

Hi snake lovers. My three year old male bull has stopped eating. He's still very active cruising around his cage frequently. Its been about a month since he's eaten. He's done this before so I'm really not that worried yet. I went to a larger rat (frozen thawed) and wonder if that might be why he's turning his nose up. Nothing else has changed in his cage. Lights and heat are on timers and the warm side of his cage is 82°F. Thanks
Carl