While sitting at 'her' desk, the new Janet shrinks from 5'2 to 5'1, and the new Dave in 'his' office grows to 5'11. Dave thinks "a couple inches aren't that much, but i want to see my shorter secretary!", so he calls her in the interphone.
Janet stands up and feel weird, but she can't quite put her finger on it, so she goes to her 'old' office.
Just as she enters it, Dave is in front of her, and she thinks "janet (me) is really short, i just have to adapt to look up at others, but i like being this short, it's just for a day though, let's see what my new old self has for me!"