system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come when you drop a totally untangled cord and then pick it up two seconds later it always transformed itself to the Gordian knot?

For example earphones.
gpt
This had been observed for many years - but never described as a scientific phenomenon until about a decade ago.  So this is relatively new knowledge for humans!

Raymer & Smiith wrote in *Spontaneous knotting of an agitated string* (PNAS October 16, 2007 104 (42) 16432-16437):

* A average string (diameter 3mm) of length less than 46 cm (or 1.5 feet) will *almost never* tangle itself up, even if you put it in a sealed box and shake it for an hour
* The stiffer your string, the less likely a knot; headphone wires, for instance, are less likely to knot than a soft string, but more likely than thicker steel wire.
* The longer your string, the higher the probability of a knot... but it tapers off quickly at around 50% (under their conditions)!  Longer strings do *not* always mean higher chance of knotting.
* The knotting happens because a knot-forming crossing is roughly as likely to happen as a knot-undoing crossing; but if a string is coiled (and thus touches itself in many places), there are *multiple chances* for a knot to form, and it's very likely that at least one will occur.