Science the Rat is Princess Bubblegum's pet rat. Finn called it a her, but it still might be male, so its gender is unknown. It appears in "Too Young" as a cameo. It was trained by Princess Bubblegum as a scientist. In the episode "From Bad to Worse," Science the Rat saves the Candy Kingdom from the second zombie outbreak of the series. For this, Science the Rat receives a medal at the end of the episode. In this episode, Princess Bubblegum mentions his name to Finn, so he could figure out the formula.
He is a candy corn rat with an orange nose, pure black round eyes, small ears, small legs, and a long tail.