Here is a page of scribbles turned into drawings. Each took less than 5 minutes. (I added the red so that the original scribbles would be easier to see for this particular drawing).
My father (who was also an artist) and I used to do these all the time, when I was young. He (and I, later) went to libraries and nursing homes and had audience members come up and make a scribble, then watch and laugh as he turned them into silly drawings.
I use this exercise in my classes sometimes, to help unleash students' imaginations.
Lynda Barry's Writing the Unthinkable workshop reminded me of this amazing exercise in creativity.