[YouTube Link]  
Someone took a drop of water that had microbes in it and shot a 250mW green laser beam through it, causing a magnified real-time shadow play of swimming translucent critters. A cat is intrigued.  
Originally described here:  
... but the site crashed from views, so the explanation is mirrored here:  
[via Miss Cellania]
:: YT comments ::
LinusMines: The cat somehow makes this video so much better.