It is a blue transparent jar with a red lid with sesame seeds inside.
Role in episode
At the Krusty Krab, Mr. Krabs holds a bun seed counting contest with the prize being a free Krabby Patty. Several fish make guesses, but none of them are correct. Plankton then attempts to guess, but Mr. Krabs does not let him and takes him back to the Chum Bucket. Plankton threatens to call the Bogus Business Bureau, but Mr. Krabs doesn't care.
The Bogus Business Bureau then arrive at the Krusty Krab with Agent Twirp saying that Mr. Krabs must let all customers guess no matter how diminutive or annoying they are. Plankton then guesses how many seeds are in the jar, using a machine to help him. He announces that the answer is 500,301 seeds. However, Mr. Krabs corrects him, replying that the real answer is 500,300 seeds, one less seed than what Plankton guessed. Agent Twirp then interrupts, stating that all of the seeds must be counted to confirm that 500,300 seeds is the correct number.
All of the seeds are counted, and the total is 500,300 seeds, like Mr. Krabs said. However, SpongeBob notices an extra seed on the lid, sadly announcing that Plankton was right.