In addition to the tap controls, you can also swipe to spell words!
Swipe across the letters in order to spell your word:
You can swipe 2, 3, or all 4 letters. Lifting your finger will not delete the already entered letters.
To erase a letter, tap it either in the circle or the in the word at the top of the screen.
You can quickly erase an entire word by tapping outside the circle.