In the scene where Nick gets upset in Frankie's room after she went with Morgan in Nick's car, there's a visible sound mic in the reflection in the window. You can see it best when he is picking her up to put her on the bed.
Right after Frankie leaves Morgan's house (storming out because of the thoughtless comment of his mother during dinner), Morgan walks down the street and then you see Nick and his buddies in the car.
The friends ask Nick if they should get Morgan and he says no, he has to go see Frankie, first. As they take off, you can see a person standing in the reflection of the car. It actually looks like James Spader (who plays Morgan.) You can see his light colored buttoned down shirt.
Frankie takes Morgan to a local club where 'Jack Mack & the Heart Attack' are playing, and there's a painfully obvious "dancing double" for Frankie. Other than a really long wig and similar clothing-they have nothing in common!
After Morgan (Spader) knocks Nick through the railing off the 2nd level in the final fight, Nick is lying on the ground below and a rope is hanging from the ceiling. At the bottom of the screen a mysterious hand reaches into the picture and pulls the rope back and swings it back out. When the rope returns the hand appears again to grab the rope.