I've no idea what exactly I did or said to make Spiro crack up... (though to be fair, moments later, she did do an impromptu caveman impression.)
I've developed this awful habit, when working with models with whom I've got a relaxed and comfortable rapport: right before I press the shutter, I say something amusing. I don't even realize that I'm doing it, until I've already done it. And doing so can put my very safety at risk as it can provoke some models to violence.
Contrast boost (+0.05) in Aperture 3.1.3