If you opened up the dictionary to "laughing to keep from crying," you'd probably find this video.
Little Julia was frightened of having the callus around her plantar wart scraped off, so she reacted by bursting into tears. But the actual process proved more ticklish than terrifying, so she turned off the waterworks and started giggling instead. Except the length of the procedure caused her to become concerned that pain was just around the corner, so she started sobbing again. However, it didn't actually hurt, so she laughed it off.
And back and forth and back and forth forever.