What is this bouncy thing in Minecraft?

While I was playing Minecraft, I discovered an underground cavern. In the cavern was a nice supply of Iron, Coal, etc. There were also skeletons, zombies, creepers, etc. Lastly, there were these little bouncing blue cubes with eyes. It hurt me when it bounced on me, and when I hit it with a shovel, it died instantly, and didn't drop anything. I have come across many of these little cubes and never has any of them dropped an object. I couldn't find what they are anywhere online or on the Minecraft Wiki. Anybody know that this thing was? What is it's purpose? (Other than to bounce around and annoy me).