This isn't a true slip-up, but it looks like one and a lot of people think it is.

In the various "flashing lights" sequences, especially at the climax of the film, the lights are supposed to be flashing at a rate of 3 per second, triggering blackouts or fits in the epileptic scientist. The lights are actually flashing at a much slower rate.

This was a "deliberate mistake" on the part of the film-makers, as they didn't want 3-per-second flashes triggering fits in the audience.