Mental Stretch

[coloradotransplant]

Read each line aloud without making any mistakes. If you make a mistake you MUST start again without going any further.

This is this puzzle
This is is puzzle
This is how puzzle
This is to puzzle
This is keep puzzle
This is an puzzle
This is idiot puzzle
This is busy puzzle
This is for puzzle
This is forty puzzle
This is seconds! puzzle

Scroll down for answer..
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Now go back and read the THIRD word in each line from the top.