Level: secondary school students. Time: 10 - 15 minutes

Prepare: you put two pictures in front of a pair of students ỏ on the board and tell them to talk about the differences

Procedure: If the students are already familiar with the concept, then you just need to repeat the "check" questions. But the first time you do this activity, it is helpful to explain the concept using the blackboard: draw two simple pictures with one or two differences and explain that partners will each receive one version. They must not show their pictures to each other, instead they have to talk to each other and circle the n differences. Check:

• Are these pictures the same? (no)
• How many differences are there? (n)
• Can you show your partner? (no)
• What do you do when you find a difference? (circle it)

After the activity, you can either provide the answers, or elicit the answers from the students, or simply tell the students to put the pictures side by side so that they can check whether the differences they found really exist or not.