What is that Thing?

What is that Thing? is the first half of the ninth episode of Season 4. It originally aired on November 1st, 1999.

Summary
Arthur and his friends separately find the same metal bobbin but don't know what it is. It happens to fit exactly what they need at the moment it appears. They argue over it and find out that it's Mr. Ratburn's bobbin and learns what it is at Mr. Ratburn's puppet show.

Trivia

 * Muffy uses the bobbin to save a plush aardvark of hers named "Andy". It wears Arthur's sweater - a clever in-joke.
 * Nemo's design has changed in this episode after his debut in Francine and the Feline, and has remained in subsequent seasons.