When we lived in our flat, Charlie lost 9, then I replaced them. Then most of the next set of 9, all the same type!!!! Then we found a few.
Some went under the fridge, so we lowered it at the front! Some went under the 3 sofas, so we put wood under the bottom of sofas, under the bed, in the bed draws. Everywhere.
When we moved they thought it was Chrstmas come early all these balls appeared.
Nicky