There are lots of ways to stretch student thinking and get them talking to each other about ideas. One fun way is through riddles that require inductive reasoning, critical thinking and hopefully some good collaboration around student ideas. The three brain teasers below created by TED-Ed have fun visuals and include an explanation at the end. All the videos also include lesson plan ideas to deepen the conversation and start discussion.
In this first video about prisoners' hats the problem set-up ends at 1:35, so stop the video there if you want kids to work on the problem before learning how to solve it.
In this zombie bridge problem the set-up ends at 2:00.