Unusual

Read the following paragraph. There is something unusal about it. Can you tell me what is so unusual about it?

This is an unusal paragraph. I's curious how quickly you can find out what is so nusal about it. It look so plain you would think nothing was wrong with it. In fact, nothing is wrong with it! it is unusual though. Study it, and think about it, but you still may not find anything odd. But is you work at it a bit, you might find out!Try to do so without coaching! You probably won't, at first, find anytthing particularly odd or unusual or in any way dissimilar to any ordinary composition. That is not at all surprising, for it is no strain to accomplish in so short a paragraph a stunt similar to that which an author did throughout all of his book, without spoiling a good writing job, and it was no small book at that .By studying this paragrph assiduously, you will shortly, i trust, know what is its distinguishing oddity. upon locating that "mark of distinction," You will probably doubt my story of this author and his book of similar unusuality throughtout. it is commonly known among book-conscious folk and a proof of it is still arounf. If you must know, this sort of writing is known as a lipogram, but don't look up that words in any dicttionary until you find out what this all about.

Don't ask me the answer, i was given this ??? question by an english teacher. But you may tried and tell me. i will check with my teacher.