Here`s my idea to talk about deduction practicing the structure must be and can`t be.
I cut some advertising pictures off magazines but it can also be made with internet images.
I showed the pictures the students and they were supposed to guess what was the product advertised. For example: they look at the picture bellow and had to make statements like this: It must be a soap advertisement because the man is in the shower. To elicit more discussion I asked questions like: Can it be a shower ad? They said thing like: It can be! After everyone`s opinion, I told the correct information. You can play with students imagination, it`s great! Enjoy!