Perry the Platypus

During the creation process of Phineas and Ferb, showrunner Dan Povenmire decided to make Perry the Platypus teal green and have him make purring noises, both because they were distinctive, and that he never did research into the biology of platypi. As it turns out, however, not only do platypi glow teal green when placed under a blacklight, but they actually do purr in real life, which leaves Dan stunned upon finding this out.

Example of:
Accidentally Correct Zoology