When Tom Felton's character Matt is using two pens to tap on a table while Troian Bellisario's character Olivia is talking to her science teacher, the blue pen starts in his right hand and the black pen starts in his left hand, but when the scene cuts back to Matt, the pens have swapped the hand they were held in.
When Tom Felton's character Matt is using two pens to tap on a table while Troian Bellisario's character Olivia is talking to her science teacher, the blue pen starts in his right hand and the black pen starts in his left hand, but when the scene cuts back to Matt, the pens have swapped the hand they were held in.