Read each Line out Loud

This was developed as an age test by the R&D Department at Harvard University .
Take your time and see if you can read each line out loud without a mistake.

The average person can't do it!
This is really difficult, not so easy, so be careful.

1. This is this cat
2. This is is cat
3. This is how cat
4. This is to cat
5. This is keep cat
6. This is a cat
7. This is fool cat
8. This is busy cat
9. This is for cat
10. This is fifty cat
11. This is seconds cat

Now go back and read the third word in each line from the top down.