Find about six or seven clear, large pictures of weird and obscure inventions that the students won’t have seen before.
Elicit and write a list of modals on the board, starting with those expressing the strongest certainty (e.g. definitely) and ending with the weakest (e.g. might, may). Besides the weakest modal, write +/-1. Go up the list, writing +/-2, +/-3, etc. The strongest modal will probably have a value of about 5 or 6.
Put the students into groups. Explain that they have five minutes to discuss what the inventions might be. Then they are going to make a sentence using a modal of probability to say what they think the invention is. E.g. It’s probably for people to catch burglars in the net.
If the students are correct, they gain the number of points written beside the modal. If they are incorrect, they lose that number of points. (Explain this before playing!)