Paradoxical instructions?
In an ultrasound exam, when I prompt patients in their bed to lie on their back - this usually happens in a moment where they lie on their right or left side or when they sit - more than half of them turn around on their belly. This is a funny paradox. It happens to my colleagues as well. I don't know why, maybe patients think: well, I am already on my back but the doc wants me to change my position, so it must be the other side he's talking about. I suppose they try to cooperate, so when they don't know what to do, they do the thing that seems to fit best. "Lie down!" works better. But say "Lie down on your back!" - and they will be on their belly.