These were interesting beasts. The camera scanned the scene, from left to right, taking a roughly 10-30 seconds to complete an exposure. The left side of the picture is finished well before the middle, much less the right, was even begun.

One "games" that some enterprising subjects played was to initially stand at the very left side, in the back row. After the camera passed there position they would duck down and run behind the others and pop up on the right. With a group this wide it was possible to put up in the middle before the camera got to that point and then run to the right.

I think these three are really the same young man. Note the change in his expression from the first to the last.