The snake who thought he was a mouse.

You know how you can make organisms resistant to disease or poison by introducing it to their system in very small amounts (immunisation). Similarly, repeated exposure to many things dulls their effects (habituation, desensitisation).

Could you not, and this is taking something of a drug-induced leap here, but could you not theoretically introduce mouse genes into a rattlesnake's DNA and over generations make it feel conflicted biological empathy for mice, causing it to not want to eat them? If you picked the primo genes, that is.

If anyone wants to fund this project, I'm definitely a proper scientist. And I'm definitely not a mouse.