Lucinda,
I think I must have Foster's twin sister. Kipper is a big, black, sleek, panther-like long-tailed cat also!
She LOVES boxes. It is her mission in life to get into any box or box-like object. It is soooooo funny when she can't quite fit and her rump is hanging out! She will also get into the dishpan, if I leave it on the floor, and the kid's backpacks, if left open. If a drawer is open, she will jump in.
She once tried to get into the shoebox my 3-year-old's shoes came in....you can imagine how small it was. She put her front paws in, realized she wouldn't fit and then gave me a disgusted look, as if to say, "What kind of box is this?!?"