Way back, years ago, we had a guy in our R/C club that could never get his engine to idle low enough to kill it, and his chosen method to do that was throwing a rag in the prop. After that, when ever my youngest son would hear a car engine still trying to run after the switch was turned off, as many of the high compression muscle cars in the 70's did this, he would holler, " Throw a rag in the prop". Our family were the only ones who got the joke. Oh well! I guess you had to be there.