Eating a snake might not kill a predator outright. And higher predators (like mammals) also have food preferences. They don't always eat stuff indiscriminately

Eating a snake might not kill a predator outright. And higher predators (like mammals) also have food preferences. They don't always eat stuff indiscriminately, so predators that don't _like_ snakes will preferentially survive. Eventually, this can get established as a genetic trait. Or as a behavioral one, if parents don't teach cubs to hunt snakes.