Tests of this kind don’t suggest that all animals feel pain. Insects are in the same large animal group (arthropods) as crabs. Insects appear to behave normally, to the extent that they physically can, even after quite severe injuries. They don’t groom or protect injured parts of their body, but keep doing whatever they were doing. Crabs and some shrimp, in contrast, will groom injured areas. You can still doubt that these animals feel anything, yes. But you can doubt that about your next-door neighbor. Skepticism is always possible, but a case is being built here.
