In the fight scene of Karl and Jon, Karl spits heavily at Jon's face. In next scene, there is no trace of spit.
Cersei refers to Joffrey as her first child. Actually, as she said in The Kingsroad (2011), she had a son by Robert before Joffrey.
Moments after Jon kills Karl, at the left side of the screen where Karl drops, it is an extremely blatant prop doll.