It was a Tupperware tub of live baby rats that made Dr Jessica Pierce start to question the idea of pet ownership. She was at her local branch of PetSmart, a pet store chain in the US, buying crickets for her daughter’s gecko. The baby rats, squeaking in their plastic container, were brought in by a man she believed was offering to sell them to the store as pets or as food for the resident snakes. She didn’t ask. But Pierce, a bioethicist, was troubled.