Foam carving for theatre is a very physical process. From creating the blocks to carving with the Kitchen turkey/bread knife. Depending on the needs of the production and time frame the foam is primed and painted or covered with fleece and hand painted, but it always starts with a form to carve.
I use photos and small figures found in children's toy stores as references when carving. I then scale up to the size I need to fit the starting block of foam.
Below is a rinocerous in process. It is important to clean the blades often with cool lube and other cleaners to keep the motor from over heating.