Painted legionary helmets?

[Tarbicus]

It's absolutely true. In visual effects one of the most difficult things to do is a convincing face replacement (substituting a stuntman's face for an actor's). The slightest iddy-bit thing wrong and the entire effect flops. Try the mask optical illusion: Get a face mask, turn it back to front, and it still seems to project outwards towards you. The brain is hardwired for facial recognition. Do the same trick with anything else and the effect doesn't work.