Human behavioral organization on queue

Sarah and I arrive at the cinema to see a screening at the film festival only to find a long line of at least fifty people out front. Being our first time at this theater, I did not know where to buy tickets. Leaving Sarah to guard our place, I follow the line to its termination at a trash can. I enter the front door to find no line at the box office.

I report back to Sarah and ask the fellow in front of her

—Excuse me, what are you waiting in line for?
—I don’t know, he says.

How did this queue form? It looked like people waiting in line, so we joined it habitually. It probably started as a few people waiting at the entrance or having a smoke; after a dozen or so people joined, the group self-organized into a queue to point where those at the end had no idea they were not waiting for anything.