I was going to suggest that it was multiple exposures. And I agree that mults should only be done for "real" with film, not with layers in PS.
If you shoot with film, underexpose, and vary the angle and distance slightly, you can actually layer up the films and get some interesting effects. Might work better with positives than negatives. Back in the early days of NDT, before the modern 3D airport-type scanners, that's how we could see through objects for real. You'd need something more powerful than Photoshop to do that with multiple digital exposures.