Except, this being an experiment, the box also had a hidden slit in the back. Thus, after depositing the balls, the experimenter could remove any number of them without the baby being any the wiser. The researchers were interested in whether an infant who had watched three balls enter the box, but could only retrieve two, would scour the box for a longer period of time than if he’d been able to retrieve all three. This would suggest he was able to mentally represent three individual objects.
Indeed, the babies did demonstrate increased scouring time (by about one to two seconds) in conditions where “balls entered” did not match “balls retrieved.” But this pattern of results only held when the experimenter deposited two or three Ping-Pong balls. When she deposited four, infants lost all expectations about how many balls would be in the box.
If that blows her mind then the Piraha people are going to put her into a coma:
and
Taken from here PDF. more information about the Piraha on wikipedia