Why Do Babies Drop Stuff?

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A tropical snack of banana and avocado chunks sits on the high chair tray. Your baby digs in. Maybe you can actually get to that cup of lukewarm coffee. But no—here comes the first splat, quickly followed by a second, third, and now the dull clunk of the sippy cup. Coffee break is officially over—it's time for some deep knee bends. It turns out that babies dump their food (and sippy cups, and toys) from high places not just because they want to watch you aerobicize or to feed the family dog (although that's fun too). "They're exploring gravity and cause and effect—it's a neat little experiment," says Dr. Lise Eliot, Ph.D., author of What's Going On in There? How the Brain and Mind Develop in the First Five Years of Life.

Infants start learning about gravity months before they are able to intentionally pitch a bit of banana overboard. A classic study from 1993 found that when 4 1/2-month-old babies are shown an object inexplicably hovering in the air, they seem intrigued: They stare at it longer than they stare at something that is clearly supported. By this age they've learned that it's unusual when an object remains stable without support.

The thrilling time comes at about 12 months, when babies will purposefully pick up an object with the sole intent of dropping it over the edge of the high chair tray. They follow its plunge intently and watch it land. And more than just "things fall down," babies are learning that things behave differently upon impact: Avocado sticks to the floor, blueberries bounce and roll, a spoon goes "bang," oatmeal goes "splat," milk "sploosh."

Of course, there's another endlessly fascinating question: Will Mommy pick up the cup if I drop it again? And again? And again? And...