The Jerktonium only appears in It's a SpongeBob Christmas!. It is a dangerous chemical element in the periodic table discovered by Plankton (no other element has been in the periodic table before). It also serves as a trap for the residents in Bikini Bottom (except for SpongeBob, of course). Since there aren't any donkeys in Bikini Bottom, Plankton uses Jerktonium in the fruitcake that is given out to everybody in Bikini Bottom. The Jerktonium causes all Bikini Bottomites to become grumpy and transform into donkeys in order to make Plankton appear to be the nicest of them all. Everyone who tries the fruitcake will be transformed into donkeys with donkey ears and a tail, a face with a muzzle, big black and bushy eyebrows, black bags around their eyes, a mass of black stubble around their mouths called a five o'clock shadow, and a head all covered in donkey hair. Their laughter will become the braying of a donkey. Their hands and feet will become hooves. They will fall to all fours and their voices will be replaced by full braying. Then they will go mad and begin braying and kicking wildly, throwing their clothes off in the process. Some of the Bikini Bottomites are fortunate enough to retain their voices for reasons unexplained. Then they are rounded up by Plankton and his minions to be taken to the pound for inspection. After they have become donkeys, the Bikini Bottomites are asked their names by Plankton going one by one as they are called. If that answer is a bray, he removes the clothes and puts them into boxes for sale. If they answer with their names, he holds them to work for him, making sure they cannot rat out for Plankton's evil plans to the authorities back home in Bikini Bottom. The residents can only watch sadly as they are forced to work like donkeys they have become. Most of the Bikini Bottomites who have transformed into donkeys are sold to the salt mines and circuses, among other clients, all of whom are doomed to a life of intensive labor. It is unknown if any of the Bikini Bottomites have ever found a way to become free from Jerktonium (that is, until SpongeBob finds a way to cure them by singing the song using the antidote), or whatever happens to the talking donkeys forced to stay at the pound. Plankton's first victim is SpongeBob, but SpongeBob is immune to Jerktonium because of his pure heart and tiny brain, causing Plankton's plan to prove insufficient yet again. (The reason why SpongeBob's heart prevents him from being infected by Jerktonium is that Plankton's plan has failed completely to suffice.) Soon Plankton gets tired and allows SpongeBob to deliver the fruitcake, causing everybody to get infected with Jerktonium and transform into donkeys.