Typos. They're killing me. I really think that the typos detection algorithm (or whatever fancy name you gave it) should be more flexible.
For example: if you type 'if' instead of 'of' you'll automatically lose a heart, regardless of how close the letters 'i' and 'o' are on the keyboard, you'll lose a heart because 'if' is an existing word.
I can give a more specific direction about where exactly can we improve it if needed.