Byzantium's Shores: chronicling the misadventures of an overalls-clad hippie

Here is an interesting mental exercise I received in an e-mail the other day. Enjoy.

:: Take your time and see if you can read each line aloud without a mistake. The average person can't.

This is this cat
This is is cat
This is how cat
This is to cat
This is keep cat
This is a cat
This is dumbass cat
This is busy cat
This is for cat
This is forty cat
This is seconds cat

Now go back and read the THIRD word in each line.