The behavioural cue of ‘flexible self-protection’ is a way to establish whether an animal feels pain, scientists say
Crickets that received the hot probe “overwhelmingly” directed their attention to the affected antenna – they groomed it more frequently, and tended to it over a longer period of time, he says. “They weren’t just agitated and flustered. They were directing their attention to the actual antennae that was hit with this hot probe.”
It depends on how you define “creature” and “pain”. There’s surely some single cell life that doesn’t. Are those creatures? Also, for plants, there’s growing evidence that many do release chemicals when hurt, which other plants and animals react to. Is that pain? I’d answer yes to both of those, but both are not hard definitions. They can be argued either way.