Resilient Sphere

Resilient spheres are bouncy, red orbs that appear the Ultima Underworld series.

Description
Resilient spheres will bounce when thrown, although their exact use has puzzled many an adventurer. These strange items can be found within Britannia's Stygian Abyss, and they appear in great abundance on the strange world of Talorus.

Trivia

 * Dr. Cat (David Shapiro) did the level design for Talorus in Ultima Underworld II, and the spheres that appear there may be a reference to his own game, DragonSpires. One of the earliest objects to be placed in the game were large red bouncy balls, and according to Dr. Cat, he and Manda Dee spent a significant amount of time manipulating these balls such that they filled a castle map before another player appeared and stabbed them.