In the 2003 film, Tess-in-Anna has to play guitar for Anna's band, but doesn't know how. So Anna-In-Tess plugs in behind stage and plays for her. Being a guitarist himself, this troper knows that muscle memory is a huge part of one's playing ability, and Tess's body would have neither the muscle memory nor the conditioning necessary to play anything more complicated than a power chord.
Not everyone would know that, would they?
Explain? It doesn't matter to the audience. In the film, though, it shows Anna-in-Tess playing the guitar with Tess-in-Anna "finger syncing". But neither of them would be able to play at all, since the mental and physical part (both important) are separated.
Rule Of Cool? It did look majorly awesome when Jamie Lee Curtis rocked that solo.
I was more confused as to why everyone cheered on Tess as Anna when she clearly wasn't moving her fingers or putting her hand anywhere near where the notes were. Is no one in the audience watching her? And even if they weren't, wouldn't the people running the contest notice that she's clearly doing the guitar equivalent of lip-syncing? It just doesn't make sense that they'd be able to fool anyone in the audience.
