Felch has two meanings, depending on where you come from (ho ho, nearly a pun, there) and what sort of sexual community you belong to.
It's other meaning does indeed refer to the practise of de-fanging & de-clawing small rodentia (typically gerbils or hamsters) and inserting them into one's bottom for the sexual pleasure derived from the twisting & twitching of their death throes as they suffocate.
Roman soldiers also used to take advantage of an animal's death throes by sodomising geese, breaking their necks at the moment of orgasm.
So there you go.
God knows how much people do actually partake of rodent felching, mind. It seems a hell of a lot of fuss to go to just for a nice feeling up your bum. Why not try a twisty vibrator? They're resuable & far better for the karma.
Dennis went to the pet shop for some felching supplies