In an assault, a character stabs upwards with a fork held in an underhand grip. When he releases the fork, however, he appears to have stabbed downwards with an overhand grip. Even if we had not seen the attack, the hand position on release looks extremely unnatural - almost as if it was posed purely for the camera angle.
When Ava is stabbed - it's in the lower left stomach, yet when you see her scar, it's up the middle from belly-button to breast bone.