While Aria is being pulled out of the crate on the train, Garrett's arm falls back to his body very deliberately and clearly displays that the actor is alive. Additionally, when the camera returns to his body, his arm is then underneath the blanket.
When Aria is seen first in the "coffin", Garrett is to her left. In the next shot, he's to her right.
Aria (played by Lucy Hale) is tied up with her hands in front of her, she could easily have removed the tape gag from her mouth. Yet she doesn't.
When Spencer and Hanna find Aria's purse on the train, "A" sends a text to Aria's phone which Spencer reads aloud as "Guess who's not gonna make it to the end of the line?" but the shot of the phone shows that it says "Guess who won't make it to the end of the line?"