Kelp Shakes are an addictive and potentially toxic soft drink served in the Kelpshake restaurant chain. They appear in and are the main plot of the episode "Best Frenemies."
The drink comes in a light green bottle with a light yellow lid and light yellow straw, and on the bottle is a light yellow label that reads the drink's name in light red text.
It is eventually proven by Karen that the drink is 99% kelp juice and the remaining percentile is an unknown radioactive material that, at the end of the episode, is revealed to make the consumer grow green hair on their entire body as well as grow abnormal round buttocks.
At the end of the episode, SpongeBob, Mr. Krabs, and Plankton are the only ones seen being the victims of the Kelp Shake. However, since almost everybody else in town drinks one, they all suffer the same symptoms.
The body-changing side effects of the beverage cover the entire body in fuzzy kelp similar to a gorilla's fur and their clothes vanish as the fuzzy kelp grows all over their bodies. For some odd reason, however, it takes everybody except for Mr. Krabs and Plankton about two days to grow green hair and round buttocks.
Because of these symptoms, the authorities order the complete shutdown of all of the Kelpshake restaurants and proceed to dispose of the dangerous chemicals used to produce them.
Role in episode
The drink was very popular and tasty, as Plankton described it as having "a pungent aftertaste." However, Mr. Krabs describes his first sip of it as tasting like a "wet gym sock" before the flavor kicks in. At one point it is so popular that restaurants are on each block of Bikini Bottom.