Makes sense to me. Liz/Beth aren't resistant, exactly, but one or the other can be more beneficial, so she should know. There are two triggers. The seven notes to the chorus of Neil Sedaka's 'Happy Birthday Sweet Sixteen' turns her around in a few seconds, flat. Basically the creepiest song ever, it terrifies whichever personality is active into switching. Leah can whistle, play a tone or recording, it doesn't matter, so long as she hears it. It doesn't have to be musically accurate, the notes work just fine. The other is holding her left wrist like you would to take a pulse, thumb on the artery.