The resource is Which One Doesn't Belong?
The idea is that there are four pictures. Each of the pictures could be the answer to Which One Doesn't Belong? Your job is to find a reason why each picture doesn't belong.
I used this as one of my Figure It Out! Fridays a little while back. I tossed this picture up on the SMART Board and asked "Which One Doesn't Belong? "
After we found a reason for each one, I tried to move on to our lesson of the day, but students protested. They wanted to do another! So, I ended up putting this one on the screen, too.
As the day progressed, it was interesting to see the different reasons different classes came up with fo a card not belonging! I like how this promotes critical thinking, thinking outside the box, and justifying your answer.
You can find plenty of these puzzles at WODB.CA. They are broken into three categories: shapes, numbers, and graphs.