Crats

What is a crat?
Maybe a fish and a cat?
Or a cat in a hat?
No.  It's a rat and a cat.

A rat and a cat.
To play with and pat.
Not a bad bat.
It's as simple as that.

A cat may be fat.
Be they'll always chase rats.
So what makes a crat?
Ask my friend Chat.

See Chat chats with rats.
He also chats with cats.
He sat on his mat.
And studied his crat.

He says "so this is a crat
One rat and one cat.
Where their skin forms rolls of fat
That's where they're connected at.

But how do they get like that?
Hell if I know."