Could the word 'fat' mean 'big'? Here is the example, which I think 'fat' seems to mean 'big'.
It was a knothole in the roof. He cocked his head to one side, shut one eye and put the other one to the hole, like a 'possum looking down a jug; then he glanced up with his bright eyes, gave a wink or two with his wings - which signifies gratification, you understand - and says - 'It looks like a hole, it's located like a hole - blamed if I don't believe it is a hole. Then he cocked his head down and took another look; he glanced up perfectly joyful, this time; winks his wings and his tail both, and says, 'Oh, no, this ain't no fat thing, I reckon! If I ain't in luck!--why it's a perfectly elegant hole!'
(from 'Baker's blue-jay yarn' by Mark Twain)