jumping bean

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A seed of certain Mexican plants, especially of the genus Sebastiania, containing the larva of a tortricid moth whose movements cause the seed to jerk or roll.

from The Century Dictionary.

• noun Same as jumping-seed.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A Mexican jumping bean.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun seed of Mexican shrubs of the genus Sebastiana containing the larva of a moth whose movements cause the bean to jerk or tumble