I saw a yorkie video on google and it showed a yorkie playing. He was trying to get a squeak toy out of a sheet. They had covered it over and he would dig and dig at it and it would squeak and he would dig again.
I thought it was a great way for them to get some exercise and play when they are bored or it is bad weather and cant get them out for a walk.
I tried this with Tommy and he wore himself out trying to get this toy out of the sheet. Of course after a while I kinda helped him find it.