Delta brainwave

Description
The Delta Brain Wave is generated by all animals (with the exception of Phillip J. Fry), all robots, and certain trees. The Brain Spawn attack the Delta Brain Wave.

Appearances
Since the Delta Brain Wave is generated by every character but Fry, it is present in every episode (as there is at least one more character in every episode).

Mentions

 * "The Day the Earth Stood Stupid" (3ACV07)
 * "The Cyber House Rules" (3ACV09) (possibly)
 * "The Why of Fry" (4ACV10)