The animals descend an inclined plane, but they don't move in an accelerated motion. They go down by awkward steps, swinging forward and back.

During the motion the position of their barycentre changes. They have only two legs and each one ends in a rounded foot. They don't slide thanks to friction between the paws and the plane.

Ducks and Hare are almost anti-educative: motion on the inclined plane, but uniform.

However easy to construct they may appear, in fact they are not. Their weight must be evenly distributed and the pace moderate, so that they will not lose their balance.

These toys illustrate the law of conservation of energy; their initial potential energy is converted into kinetic energy (only a little), the rest is friction.

Also, such toys show that the (uniformly) accelerated motion down the inclined plane is only a theoretical model. In fact, as Newton observed, in all kind of motion the dissipation forces are at work (the friction, viscosity, air resistance). Due to them, in static systems, instead of an accelerated motion we observe steady a uniform (i.e. with a constant velocity) motion.

We can calculate how much of the heat is released per a single step. If the little elephant weighs 200 g and it takes it 20 steps to descend 10 cm, it is almost 10 mJ, or 2,4*10^-3 cal.