oo wrap up bingo game

At the end of my lesson on oo; I get the children to write down 4 words that have 'oo' in them. I then show these pictures one at a time. If they have the word that matches the picture on the board; they can cross it off. Another way of playing this game is; I get the children to think of some oo words that I haven't thought of. If the picture that matches their word is shown; they lose 1 point. The children with 4 pictures left at the end; win. A way of getting the children to REALLY think.