If you've got a microscope and some food coloring, your life is about to become awesome. By carefully depositing droplets of food coloring on a specially prepared glass slide, you can watch the food coloring wander around the slide, looking very much like microorganisms chasing and eating one another. The effect is beautiful, if just a bit weird. Watch Derek from Veritasium explore the beautiful world of food coloring:
For much more on this topic, check out this page of videos digging into various aspects of the science involved.