This is actually not uncommon with snakes. There was an elderly woman in Maine known as the "Snake Lady" who did all sorts of experiments with snakes. Saddly she was bitten by a cobra while doing a cover shot for People Magazine and died.

She discovered that uneaten prey left in with a snake would remain uneaten while the snake would strike and eat any other prey item introduced. And that reintroducing the original prey item only worked if a week or so had passed first.