A Woman in Red; A Sea of Twins
Back in 1999, there weren’t as many special effects and they weren’t as insane as they are today. The producers had to get creative with how they were going to make the scenes work. Remember the woman in red? Of course, you do.
Source: Imgur
It was during one of Neo’s training sessions that a lovely lady in a red dress walks by as Morpheus is talking to Neo. It was all a show of how dangerous it is to be distracted. Anyway, around the woman were many “copies” of the same people. But that wasn’t a computer effect. The filmmakers actually hired many sets of twins. The result was the effect of Neo and Morpheus walking through a computer simulation.