"A Thunk is a beguilingly simple-looking question about everyday things that stops you in your tracks and helps you start to look at the world in a whole new light." http://www.thunks.co.uk/
Want examples?
- Is there more future or past?
- Is black a colour?
- If I switch the lights off does the wall change colour?
- If you are caught in a thunderstorm will you get wetter if you run to shelter or if you walk?
The independent thinking website has lots of ideas about thunks, as well as other cool stuff. They even have their own Youtube channel.
It's all about supporting and motivating students to think independently.