After typing "fuck", which gets replaced to "duck" when you continue on, backspace to the end of the word, and iOS4 will hover a new bubble that "asks" if you w

After typing "fuck", which gets replaced to "duck" when you continue on, backspace to the end of the word, and iOS4 will hover a new bubble that "asks" if you would like to undo the correction, as well as list any other suggestions that may be relevant for that case. This is a quick way to train the algorithm into learning your spelling habits.