In 1972, a 12-year-old boy was brought to the hospital with so much rectal bleeding that it had tainted his poop pink. Doctors kept him for four days, unable to figure out how so much blood was getting into his stool. After questioning his mother, they found out one change in the boy's diet: For the past days, he had been enjoying Franken Berry, the brand-new cereal. So as an experiment, the medical team fed him some more Franken Berry -- because the '70s were a bit more lax about the whole "testing possible dangerous chemicals on children" than we are. And what do you know? Quickly thereafter, his poop turned bright pink again.
The condition became known as "Franken Berry stool" amongst doctors, who noticed a lot more children rocking up to their clinics seemingly shitting blood.