The speaking sponge is an object that appears in the episode "Sea-Man Sponge Haters Club."
It is an ordinary kitchen sponge.
Role in episode
Throughout the episode, the We Hate SpongeBob Club uses Speaking Sponges to decide who gets to speak at any point. Mrs. Puff is the first to get one, and she tells a story about SpongeBob hijacking a boat during a different student's lesson and destroying her boating school. After she is done, Bubble Bass requests a speaking sponge and tells a story about SpongeBob ruining his meal because it's not perfect. Plankton receives one next and tells a story about SpongeBob breaking into his lab while he is working.
At the end of the episode, SpongeBob volunteers to be a speaking sponge, and Incidental 154 uses him to tell his story.