Continuity mistake: When Aria's dad drops her off at school, the camera angle out the passenger window shows her wearing blue jeans. Once she's out, the camera angle changes and she's wearing black Levis.
Continuity mistake: When Spencer beats Detective Furey at ping pong, he throws his paddle down on the table in frustration. The paddle then immediately moves to a different position in the next shot.
It Happened 'That Night' - S3-E1
Character mistake: Emily's mom tells Emily that reporters were there to talk to them about "Emily's missing remains." It's supposed to be "Allison's missing remains." (00:17:00)
In the Eye Abides the Heart - S7-E15
Continuity mistake: After Paige asks Alison if she loves Emily, the hair on Alison's right shoulder moves a few times between shots without her touching it.
Continuity mistake: When Mrs. Hastings is on the phone abut the tree in the garden, her phone is not in call mode.
If at First You Don't Succeed, Lie, Lie Again - S1-E15
Continuity mistake: When Spencer and Emily are done eating pizza, Spencer stacks both their plates. However, when Emily storms off, the plates are unstacked again and now there is a napkin on her plate.
Picture This - S2-E9
Continuity mistake: When Hanna and Caleb are sitting on the swings in the park, the first part of the scene shows nothing in Caleb's lap. However, when it cuts to them holding hands, a pizza box appears. (00:29:10)
Shadow Play - S4-E19
Other mistake: When Ezra takes Spencer's file from the school he takes it from section A-E. Neither of Spencer's names fit into that category.
Continuity mistake: When Emily and Alison are talking about Paige, the amount of water in Emily's glass changes between shots.
Continuity mistake: The position of the Bluetooth sniffer changes in Emily's hands 2 shots after Aria passes it to her in the car.
Continuity mistake: Sydney's coffee changes position 3 times after Emily sits down to talk to her before picking it up to leave. Note the creases on the cardboard of the cup.
In the Eye Abides the Heart - S7-E15
Continuity mistake: In the second scene with Emily and Pagie at The Radley, Emily's hands are constantly switching from her glass to away from her glass between shots.
The Glove That Rocks the Cradle - S7-E16
Continuity mistake: At the very end of the episode, the handwriting on the gravestone and the size/shape of the gravestone that's drawn in the comic book completely change between shots.
Cat's Cradle - S4-E3
Continuity mistake: When Hannah is on the phone to Emily, Hannah pours a glass of fizzy drink (coke or whatever) and is about to drink from the glass, in the next shot she takes the can and walks away and the glass isn't seen again.
Continuity mistake: When Fury and Spencer are playing ping pong there is one scene where Fury is holding the ball and Spencer is empty handed, then as the scene progresses Spencer is also holding a ball.
Continuity mistake: When Jason first appears in the show he is played by Parker Bagley and is portrayed as a proper, motivated and well held, wide structured man, but disappears for a season or so, and is replaced by Drew Van Acker, and is now portrayed as a paranoid druggie, with mental health issues, and a lanky skinny structure.
Continuity mistake: Hanna and Alison are at Hanna's home, when the bell rings. Hanna takes a look through the window directly next to the door, and claims it's just Travis. When she opens the door and goes outside, there is no window visible. At least not any kind that could have seen Travis. It seemed to just have disappeared mysteriously. The transition of shots between the set of hanna's interior and exterior is done very poorly. (00:12:10)
Continuity mistake: Mrs Sullivan circles "nosey bitches" on a paper (someone's file) and the circle is overlapped at the bottom. When the camera moves out the circle changes and is disconnected from the top instead.
Continuity mistake: When Lieutenant Tanner has all the Liars lined up at the station, she says that she's giving them a chance to tell their side of the story before her side becomes the only side. As she says this, Aria can be seen scratching her head in the reflection behind Tanner. In the next shot however, both Aria's arms are suddenly folded.
In the Eye Abides the Heart - S7-E15
Other mistake: In this episode, and a few episodes afterwards, Aria's phone's battery is at 76% every single time she looks at her phone, until finally dropping to 70% in episode 17 of season 7.