Maybe

"Oh great, now I have to worry about getting Kuru from eating Mermaids." Barnabus groaned.

"We would if they were real." Theodore replied in an exacerbated tone.

"But hypothetically though?" Barnabus speculated. "I see them as a totally different species. Kind of like eating a chimpanzee, you know it's related, but it's not cannibalism. Not that I plan on eating a chimpanzee either."

"You can still more easily get a disease from eating chimpanzee or monkey meat compared to other meats; mermaids would be the same, hypothetically." Theodore added. "You would still be at risk from Prion diseases like Kuru. However, you would be safe from Kuru specifically if you didn't eat the brain."

"Yes, I'm aware of that but I'm saying it wouldn't be cannibalism." Barnabus replied in an agitated tone. He didn't like it when Theodore showed he was smarter than him.

"Well, technically," Theodore started again, "by the dictionary definition, you are correct. But many laws about cannibalism are put in place to safeguard against Prion diseases, so legally it depends on the country and if they think the risk is high enough to add Mermaids to the list."

"Well then, if they ever discover mermaids, I suppose we will get to see this debate from the USDA and the FDA." Barnabus shouted in defeat.

"Excuse me, I couldn't help overhearing your debate. I think I can provide an answer. But we will have to move you to our private dining table, and that has a gratuity of $300." The sexy waitress interjected.

"DEAL!" Barnabus shouted like an excited schoolboy, taking a fistful of $50s out of his wallet and thrusting it towards the waiter. "Shut up and take my money! No wait, don't shut up, I want the answer." He whined like an impatient toddler.