I didn't think about it again until Wednesday night, when I went downstairs. As I connected my iPod to the speakers:
Me: "What? You were fine all day."
Back: "*whine* I hurt now. You should skip exercise."
Me: "So walking to and from work, up and down stairs at work, and sitting for several hours is all fine, but ... what ... you were thrown out by plugging in an iPod?"
Back: *whimper* "I'm stll weak from Monday!"
Me: "We didn't do anything unusual Monday either! And, hey, it was my other side that hurt on Monday."
Back: "Oops, was it? Oh I mean, owwwww nooooo don't exercise."
Me: "Shut up. Big baby." *starts exercising*
Back: *pouts, whines vaguely, finally gives up and admits it's fine*