Sort your mechanisms according to your own secret categories, which your are not to reveal to anyone outside the group.
Each of the mechanisms should belong to only one category.
If there are mechanisms that don’t fit neatly into any category, suggest a new category called “things that don’t fit.”
Try to make these categories easy to guess – the rule for each category should be pretty obvious.
Put each category in a separate pile or area on the table, with a Post-It™ nearby. On the bottom side of the Post-It™, write down the rule for that category, such as “Things that cut.” Then gather the class around each table to see if others can guess the categories.