It happened on my first airplane flight when I was two. Obviously, I had laughed before then, when I was delighted, or tickled, or even just because everyone around me was laughing and I knew that was a good thing.

My mother, who sat next to the window, held my baby sister and my father, who had the aisle seat, held me on his lap. This was the early sixties, when people still dressed up for airplane flights, and Dad was in a business suit with a dark jacket, a crisp white shirt and tie. Once we were airborne the stewardess came by, and my father asked if she’d bring me a cup of orange juice.

My sippy-cup, which I had mastered, was left behind. I did not know the word “trepidation” at that age, but that’s what I remember feeling as the stewardess returned holding out a small, white paper cup brimming with cold, sticky orange liquid. At my father’s urging — I think he said something like “show everyone what a big girl you are.” — I very cautiously took it, tilted it, and missed my mouth, emptying the entire contents onto him — tie, shirt, jacket — all of it.

I don’t remember what was said afterward, probably just the usual kerfuffle of the stewardess saying, “oh dear,” and Dad being mildly dismayed. The stewardess said she’d go get some napkins, and Dad added, “bring another cup of orange juice.”

And that’s when I lost it, not to a tantum, but to a rising boil of helpless giggles. “Deadpan” was another term I didn’t know, but that’s what he’d been. It was obvious to me I would just spill it all over him again, but there was my father, blandly, even cheerfully asking for yet another cup of orange juice to get poured onto his silk tie.

I could not stop, and the sight of the stewardess walking towards us, with her polite smile, holding out another brimming orange juice just made it worse. At last, she stood before us, offering me the cup, and that completely undid me to where I wriggled and screamed in Dad’s arms, helpless with laughter, and at the same time, aware that this had never happened before, that now, at last I got it. I understood why grown-ups laughed, and that laughter could seize someone as uncontrollably as crying did, except it felt good.

Honestly, I did my best. Once I’d regained control, I tried again and spilled it, and no, I was not trying to be funny. I was just as badly coordinated as most toddlers and trying to drink something from a non-sippy cup on a moving plane. I’m pretty sure we all gave up after that, and I was left in peace to giggle myself into exhaustion against Dad’s damp shirtfront. It was possibly the only time in history passengers on a plane were disturbed, not by a wailing baby, but one who was shrieking with laughter.