For the screaming to stop.
That was awesome, right? It looks like a regular face, and then it turns out it was only the inside of the ma-- wait, you're saying it didn't fool you for a second? Well ... we don't want to alarm you, but...
Collaborators from the Hannover Medical School in Germany and the UK's UCL Institute of Cognitive Neuroscience found that there is a very specific subgroup of people who are totally immune to the cerebral fuckery of the hollow mask illusion: schizophrenics.
A study found that most of us are woefully ill-equipped to defeat the mask's trickery, falling for the illusion an absurd 99 percent of the time. Schizophrenic volunteers, however, revealed themselves as the Michael Jordans of hollow mask detection. They were only fooled about six percent of the time. So while schizophrenia is a horrible affliction, at least suffers can boast one bona fide if extremely limited superpower.