We had inherited a pathetic, vaguely cow shaped prop from another high school. It featured spindly legs, a rectangular body, peeling masking tape, and a broken knee that was held together loosely with tape, glue, and 13 different kinds of fasteners.
(The black goo in this photo is a version of Great Stuff that is used to mend ponds, I was using whatever I could find on sale)
I did not know that different cans of Great Stuff would have varying expansion rates (perhaps related to the age of the can?). I was surprised to come in one day to find that all of the foam I had used the evening before had expanded twice as much leaving Milky's head to look more like a chipmunk with huge cheeks and tiny slits for eyes. I had to peel off the muslin and carve quite a bit of foam to reshape her head into a more bovine shape.