Here's a paper on the topic: "Spontaneous knotting of an agitated string" [1] From the abstract: "We performed experiments in which a string was tumbled insid

Here's a paper on the topic: "Spontaneous knotting of an agitated string" [1] From the abstract: "We performed experiments in which a string was tumbled inside a box and found that complex knots often form within seconds. We used mathematical knot theory to analyze the knots." [1] http://www.ncbi.nlm.nih.gov/pubmed/17911269 http://www.ncbi.nlm.nih.gov/pubmed/17911269