cat's cradle

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

• noun A game in which a string is looped on the fingers to form an intricate pattern between a player's hands that can be successively varied or transferred to another player's hands.
• noun An intricate pattern.

from The Century Dictionary.

• noun A children's game in which one player stretches a looped cord over the fingers of both hands in a symmetrical figure, and the other player has to insert his fingers and remove it in such a way as to produce a different figure. Also called cratch-cradle and scratch-cradle.

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

• noun A children's string game
• noun idiomatic Any complicated structure which appears to be without purpose.

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

• noun a game played with string looped over the fingers