Alex and Shakira sing a duet by themselves in the sub station. There's no one around to play instruments, yet instruments are heard. An acapella (vocals only) version of the song should have been dubbed in instead.
Kelbo and Shakira and supposed to be wearing the same clothes and accessories, as they are the same person. Yet the green shirt (with leather jacket) that Shakira's wearing has a beaded waistline, while Kelbo's shirt doesn't. Also, Shakira's wearing earrings, but Kelbo isn't.