King snake kills but won't eat

[pshisbey]

HELP! I've got a 3', 3 year old CA King that is RAVENOUS and kills fast but won't eat. Last ate successfully over a month ago. Since then it has killed 5 mice but hasn't eaten. This is very uncharacteristic; it has been a very good eater. After killing a mouse it unwinds and then starts sniffing/searching around like it CAN"T FIND THE MOUSE and eventually just abandons it! The only thing that has changed is about the time it ate last I put a piece of tree bark (from outside) in his tank, but have removed it about a week and 2 mice ago. Thinking perhaps it's something in the tank so am going to try cleaning the tank. PLEASE HELP. Thanks