A slip of the tongue
"An octopus floated by, and Little Whale called out, 'Can you help me to sing?' But the octopus just changed colour and danced away, moving all his eight testicles."
"Mummy, what's testi...?"
"TENTACLES! Sorry! TENTACLES! Those are the octopus' legs!"
"Oh."
"Mummy, what's testi...?"
"TENTACLES! Sorry! TENTACLES! Those are the octopus' legs!"
"Oh."