system
Given the following post, respond as if you're commenting on Reddit:
human
Why do cats go limp when their scruff is grabbed?
gpt
The scruff is primarily used in two situations.  1) when a mother cat moves her babies and 2) mating.  It's easy to see how injury to wigglers in the first case and lack of reproductive success in the second case may have influenced the strengthening of this response among the cat population.