1. In a large saucepan over low heat, melt peanut butter, butter, and marshmallows, stirring until smooth, about 5 minutes.
2. Remove from heat; stir in a few drops food coloring, then add cereal.
3. Coat a 9 x 9-inch pan with cooking spray, then spread mixture evenly in the pan. Let cool 20 minutes.
4. Invert pan on a cutting board and slide out the cooled square. Cut it into about 8 long rectangles.
5. Mold each rectangle into the shape of a snake and press in 2 raisins for eyes and a pointed sliver of fruit leather for the tongue.