What LEGO pieces have "real-world" functionality? I have noticed that there are a few LEGO pieces that also function in the "real-world." For example, the  10830c01 Magnifying Glass can actually magnify. 


Another example is the 70001pb01 Compass, which works the same way you'd expect any "real-world" compass to function. (Although it's not always 100% accurate.)

Are there any other LEGO pieces that have "real-world" functionality?
All Aboard!

I'd like to add my all-time favorite LEGO piece:


x870cc02, THE BLACK WHISTLE!




The white brick is a microphone. Attach it to your train's motor and BLOW THAT WHISTLE!  Depending on how short (or LONG!) your whistling was, the train would go forwards or backwards. 


Real-world use: Not only did it drive your train round the bend, but your parents too...!