I'm willing to bet quite a lot that Legend's explanation is correct. I'm especially willing to bet on Legend's explanation because my friends and I proved that's true a while back lol. If the person in the middle consciously remains relaxed it's just as hard the second time, no matter what. The person in the middle tenses up the second time due to the expectation of the second lift being different. They don't even have to know the trick for them to do this. Whether you recite an incantation or put your hands over their head, they are going to tense up knowing something is going to be different that time.
Edit: I should point out that the video shows this very clearly. Look at how the guy in the middle bends the first time, but the second time remains stiff.
