The invention of Silly String was a complete accident that nearly didn't happen.
Rex, Tiny Fox Lab

Silly string was accidentally invented when Leonard A. Fish, an inventor, and Robert P. Cox, a chemist, were testing different nozzles for their “foamable resinous composition,” which was intended as a spray on instant cast for broken or sprained limbs.Tiny Fox Lab Facts

Preview photo credit: Rex, tinyfoxlab