The researchers were out in the parking lot, and they were counting people as they came in and out of the store, and they noticed that when the volunteers stood in front of both doors, people stopped coming out of the store at all.
Os investigadores estavam  no parque de estacionamento e contavam as pessoas que entravam  e as que saíam da loja, e repararam que, quando os voluntários se colocavam em frente das duas portas, as pessoas deixavam de sair da loja.