Splinter in "Teenage Mutant Ninja Turtles," e.g.

RAT

This small, often unwelcome rodent shares its name with a lab animal commonly used in scientific experiments.

This clue plays on the name of Splinter, the wise rat sensei from Teenage Mutant Ninja Turtles. The word "e.g." hints that Splinter is an example of a rat—since he’s literally a giant, mutated rat in the series. The answer is simply "RAT," using the character as a clever way to clue the animal.