गूफ़

When Mara is picking the lock for the 3rd floor with the other 4 girls, you can clearly see that the chain is simply draped over the bars.

When Alex first enters the school, you can see the framing of what is obviously a fake movie set wall reflected in the glass of the trophy case behind her.

Cecelia (the blind girl) has a tattoo on her right forearm near the elbow. People normally get tattoos to be able to look at them. Being blind she would have had no way of knowing (unless someone told her) if the tattoo was the design it was supposed to be.