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 forty  cat
11. This is seconds  cat

Now go back and read the third word in each line from the top down, and I bet you can’t resist passing it on.