Revealing mistake: At the start of the movie it's night and raining, but you do not see any drops of water hitting a surface anywhere although/but things appear to be wet.
Revealing mistake: Frank is put in Block-D. Then one guard comes and slides open the door, and light pours onto Frank (who is curled up in the corner). It goes to a shot of the guard standing behind the bars, which he has not yet slid open. But in the previous shot when the light was on Frank, there were no shadows cast from the bars - there should have been. (00:31:55)