I made several sausage dog excluders in various fabrics in my teens. From memory all that was needed was to slope off one end to make a snout, add four smaller sausages as legs at the sides and two teardrop-shaped ears, plus two googly eyes, one button nose and a red felt tongue. No pattern was used. A snake would need a curved slope-off for the front and a tapered tail, but wouldn't need ears and legs, or, for that matter a nose. Just googly eyes and a felt forked tongue!
My friends have a great draught excluder - it's designed to look like a London underground tube train of three carriages, but I am sure that was a purchase.