Other mistake: After the Smith's house blows up both John and Jane's white shirt's are really really dirty but when they're driving in the stolen van their shirts are bleach white again except for the blood stains.
Other mistake: In the scene where Jane and John race home, we see Jane smashing her Mercedes C320 wagon into John's Lincoln town car. Both these vehicles have airbags, yet they do not deploy upon the impact between the two cars. (01:07:25)
Other mistake: In the hunt out in the wilderness - where Jane looks in the binoculars - there is a cover on one lens - but it shows you can see both sides. (00:30:27)
Other mistake: When Jane is driving with John on the roof, she jumps out when John breaks through the window. The car then proceeds to accelerate through the trees and into the air. The road is not downhill and Jane didn't place anything on the gas pedal.
Answer: She notices that he shakes his right leg twice after peeing, just like her husband.