This is not a feature effect by any means, but as a throw-away impromptu you can’t go wrong. If
someone has laced shoes with long-ish laces you are good to go. Phase one sets up the second phase
which leaves your spectator with permanently linked laces.
The bonus effect of ungimmicked
self-tying laces is a bit iffy, I have trouble keeping it set as I walk around but you can be 90%
set and complete it discretely.