Clicking

No matter how hard she wished, Pia could not successfully get her swing to swing. She would flail her legs wildly. She would bend and stretch and lean her body forward and backward, left and right. She would shake her body, twist her hips, jerk her behind, and contort her body into various shapes. All to no avail.

The swing and its chains just shrug and twist with her for a few moments, and then settle back to their quiet state, their now sullen passenger being forced to -- once again -- ask someone to help push her.

Then all of sudden, after months of such struggle and helplessness, something clicked.  Anatomical coordination fell into place and she can swing. 

Now she swings as long as she likes; a graceful, happy, bobbing pendulum.