Sometimes I am such a proud daddy. The other day my little boy Rik, age 2, contributed to science with the following insightful analysis:

Scene: The Kitchen. Dad is clearing off the table. Enter Rik holding his big cuddly Snoopy dog by his hands. Rik: “Daddy?” [holds up Snoopy for inspection] Dad: “Yes?” Rik: “Snoopy has hands. He can say ‘bye’ with ’em.” Dad: “Yes, that is true.” Rik clutches Snoopy’s hand and waves ‘bye!’. Exit Rik, exit Snoopy. 

Look daddy, hands! (source)

I was enthralled. My boy is a genius! This little peek into a toddler’s still firm grasp of the world showed me what may be an essential piece of the puzzle: A wave is a wave because it is made with a waving hand. In other words, if something does not have hands it can not wave. Or rather, we can imagine seeing a wave only if we can imagine seeing hands at the same time. That seems to me to be a fairly useful prediction. Rik produced his first falsifiable hypothesis!

It pulls back an old Garfield cartoon into my memory. It features a snowman that may or may not be seen as waving. Garfield slaps the twig that serves as his arm and walks on. The twig keeps waving back and forth. Jon comes by and waves back automatically to the snowman. Then it dawns on him it is just a snowman. But I can not find the cartoon anymore, so if anyone out there has it I would be very greatful if you could send a link? Anyway, the same point can be illustrated with the following images

Do you perceive this snowman as waving? Perhaps not.

If the snowman gets hands, does that make it more likely that you see the waving?

For those of you who are unimpressed at this time: Not everyone would perhaps predict the same. In his 2004 book Adam Kendon hints at the possibility of creating an animation of a waving amoebe, by controlling the movement features of a amoebe-like shape. I would predict that this will only work if the amoebe gets hands or something that resembles them just enough.