One of humanity’s greatest attributes is curiosity - our need to seek out and understand something. In no other is that need greater and more enthused than in children. Their boundless wonderment at even the smallest new experience makes them in and of themselves a curiosity.

I missed my usual train today, held up in meetings and paperwork. The result is my unusual placement on the last service home. It's late, and the carriages are largely empty. A few passengers several cars either way enter and leave, and disappear from view. You might expect a story of some wandering vagrant, or a drunk spinning a nightly yarn. But no. The extraordinary thing about this train is its length.

As it arrived, I noticed it. Dozens of empty carriages sped past until finally coming to a stop. Many more followed, so far into the tunnel I couldn't see the end. In any case, it was the last of the day, and I dared not miss it, so I boarded, and took my seat in the middle. A boy passed me, running from one end to the other. I paid him no mind – he didn't bother me, and made no noise. Then, maybe 20 minutes later, he returned, heading in the opposite direction.

He has made his journey back and forth so many times I've lost count. He's started giggling now as he runs down the aisle. No doubt he's made a game of it, with some peculiar rules that only a child could think up. I've made a game of it myself, as I watch him amble up and down. I've been timing him. The travels are long, relative to what you would expect for a person running through a train. The most recent, however, have been getting steadily shorter.

And now, as he wends his way down again, I spot a small item in his hand. A simple toy, stained like many a child's toys are. His laughing is louder.

Again he returns, a second item in his hands. A red spot dripping from it.

Each time his trips are shorter, and he carries a new prize.

Now there're merely minutes between passings, and he eyes me as he crosses. I look closer. The collection he carries... Is that a finger?

He pauses, catching me inspecting his horde. He smiles. A wide, open smile. A deep, sanguineous ooze spills from inside, staining his lips and dripping into a pool around his feet.

“I'm very curious to see what treasure I'll get from you, Mister,” he says with a dead-eyed stare, before running off again, his gleeful, childish giggles echoing long after he's gone.