Jason didn't understand why Lea was doing this to him. He took her at her word when she said the initial body swap was an accident, and he believed her when she said they'd be able to switch back in a week. But then there were all sorts of conditions. She told him not to gain a single pound; if he did, she'd refuse to switch back. As a result, Jason had been maintaining a strick workout routine while in Lea's body. Of course, what he didn't consider was that muscle actually weighs more than fat. It may not look like he was gaining any weight, but when the week ended, Lea would be sure to put him on a scale.