Usually, typing mistakes are easy to find (if one looks for them of course) as they make the word look unusual. There are some though that change one word into another. Sometimes, the change of the word doesn’t change the meaning of the phrase though. These are the most difficult to find typos.
I make one of these pretty often. Instead of “global warming” I type in “global warning”. The toughest one to find, but I don’t usually bother.