Swap the piping tip on the bag of white buttercream and secure a
small grass tip (like a Wilton 233). Start by filling in the chin and around the mouth with short buttercream fur. Then work on the muzzle. Make long, arching lines of buttercream starting at the nose and going toward the edge of the cake. This can take a bit of time, so be patient and give your hand breaks as you go. If you notice the heat from your hands is melting the frosting and changing its consistency, wrap the piping bag in a couple of layers of paper towel or in a thin kitchen towel.