Do crabs, octopuses and fish feel pain? Should they have greater rights to humane treatment?

In the verses of Nirvana’s haunting track Something in the Way, Kurt Cobain offers the unremarkable cliche “it’s OK to eat fish, cos they don’t have any feelings”.

It was probably meant as a metaphor, for what we’ll never know, but is it actually true? And if not, how has the belief…