Milk is a beverage that first appears in the episode "Plankton!"
Role in series
After SpongeBob tells Patrick some of his secrets to try and make him show him what is inside his secret box, the latter refuses, saying that while the former is an open book, he is more complicated, adding that "the inner machinations of [his] mind are an enigma." Patrick then imagines a live-action carton of milk spilling itself on a carpet.
Patrick drinks solidified seahorse milk, as well as determines that SpongeBob has been doing the Dirty Bubble challenge for a week using it.
SpongeBob drinks snail milk before bed.
Plankton tells a story to SpongeBob in hopes of making him cry. Near the end of the story, Plankton spills a carton of milk that SpongeBob placed, making him cry when he finishes the story. This is a reference to the idiom "don't cry over spilled milk."
SpongeBob drinks milk to help him go to sleep, although the milk comes out of his holes and he tries different methods to cure his insomnia.
SpongeBob and Patrick use a giant bottle of milk to promote their babysitting company, and also to carry smaller bottles to feed to the baby.
- Milk on Wikipedia