They both have a long tail, which helps the squirrel to balance when jumping from tree to tree, and the same large eyes, small ears and powerful back legs.

I did a little web searching and found one site that claimed a squirrel USES its tail to communicate.

I had always assumed that the reason a squirrel had a big bushy tail was that as they careened through the space between branches they used it to wave around and keep from tumbling out of control.