One of the discussions that come up from time to time when talking about paper engineering is allowable materials. Can you use string? What about cocktail sticks or skewers? I have come down on the side of pure paper apart from the occasional coin to add weight and maybe a rubber band for tension. There are a few models on the site that use coins as pendulums. Among them, the nodding cow.

The Mk I pendulum powered cow uses a coin concealed within the cow’s body to make the head nod up and down when the cow is moved. (Moo-ved?)

After a suggestion by Michael42er I released the MkII Pendulum Cow which also had a swinging udder. You can download and try both these models by clicking on the images

Check out the various other pendulum powered models by clicking on the butterfly image here.