Unusual: What's not there?

This is an unusual paragraph. I'm curious as to just how quickly
you can find out what is so unusual about it. It looks so ordinary and
plain that you would think nothing was wrong with it. In fact, nothing
is wrong with it! It is highly unusual though. Study it and think
about it, but you still may not find anything odd. But if you work at
it a bit, you might find out. Try to do so without any coaching!