You take a length of thread, in front of the spectator break it into several pieces. You roll them into a ball and then pulling on the ends the thread has been fully restored to a single length. This can then be handed to the spectator as a souvenir or for inspection.
Gypsy Thread is an old trick dating back to 1584 and now Aberdeen Thread makes the effect clean, easy to prepare and the online tuition included covers multiple routines including a 100% impromptu presentation.
Included is the online instruction and enough Aberdeen Thread for hundereds of performances.