Revealing mistake: In the first scene where Natalie is checking her phone whilst driving, you can see the gear stick is in the park position and the speedo is on zero, suggesting the car is on a trailer for this driving scene. (00:01:55)
Revealing mistake: In the scene in the lecture hall, the handrail on the steps to the left of stage makes no sense. If built correctly, which they are not, it would indicate there is a wall behind the back row and the steps are just at or below head height of the people there which makes no sense in this auditorium design.
Revealing mistake: When the helicopter is escaping with The Rock and his ex-wife, the helicopter doesn't cast a shadow or a reflection on anything it should have.
Answer: You haven't missed anything. After the successful CPR, Blake is still wearing the two heart necklaces, but a considerable amount of time passes between then and when Ben gives them back to her, so we can presume that the necklaces had fallen off at some point in between. Since Blake had taken it upon herself to wear her sister's necklace with her own, the two chains could have been clasped together (which I've done myself), as if one.
Super Grover ★