Zoe Butler was amazed to find a pair of eyes staring up at her when she opened the can of Princes tuna chunks.
But the Natural History Museum said that the head probably belonged to a Cymothoa exigua, or tongue-eating louse. The parasite lives inside a fish, entering through its gills and attaching itself to its host's tongue.
"I opened the top of the lid and saw a purply thing, a gut sack or intestine -- then I turned it round and pushed it with a fork and saw it looking back at me," she told the Nottingham Post.
"It's got like a spiny tail along the bottom -- it's quite grim.
"I dropped the fork, jumped back, screamed a bit and shouted for my nan to come and have a look."
She added: "I haven't shown it to the kids because they might get put off eating tuna.
"I just want to find out what it is and to make sure it doesn't happen to somebody else.
"I didn't set out to get compensation and I don't a want lifetime's supply of tuna!"
Mrs Butler's grandmother Susan Goddard, 69, said: "It's a little red and has eyes, bright black, looking at you. We did manage to ascertain that it was dead."
The head probably belongs to a Cymothoa exigua:
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