Can You Figure This Out?

Here is a riddle:

Railroad crossing, watch out for the cars. Can you spell it without any "r"s?

What is wrong with this paragraph?

How quickly can you find out what is unusual about this paragraph? It looks so ordinary that you would think that nothing was wrong with it at all; and in fact, nothing is. But it is unusual. Why? If you study it and think about it you may find out, but I am not going to assist you in any way. You must do it without coaching. No doubt if you work at it for long, it will dawn on you. I don't know. Now, go to work and try your luck.

This puzzle is courtesy of the Klutz The Encyclopedia of Immaturity.