Readers of this site might be interested in the following paper appeared in the Proceedings of the Royal Society and has received considerable attention in the media:
The roles of impact and inertia in the failure of a shoelace knot
The paper discusses a mechanism for the the accidental untying of a shoelace knot that many of us, including me, experience on a daily basis. The failure is sudden and catastropic as can be seen in the following video:
https://www.youtube.com/watch?v=_-aiynIphTw
and news article
http://abc7news.com/science/uc-berkeley-study-shows-why-shoelaces-come-untied/1862327/
We hope the work inspires further works on the topic of physical knots.