You can read about supernormal stimuli on Wikipedia, but, to cut an interesting story short, a super stimulus is all about how animals respond to sensory stimuli in a kind of compulsive fashion. The common example is mimicking a mother bird returning to the nest and then all the chicks open their mouths.
Now, perhaps we don't walk round with our mouths wide open when we see an attractive member of the opposite sex (well, not all the time anyway), but we are subject to the unconscious mechanisms of being stimulated by things we see, hear, eat and touch. Another interesting neuroscientific phenomenon is the way our conscious minds invent stories to account for our behaviour and, if you combine this with the effects of super stimuli, you have a heady recipe for doing things you didn't think you wanted to do and then rationalising it later. Think about that cake, movie, flirtatious response - there's always a good reason after the event, even though you didn't really want to do it.
Perhaps I'll leave it there, but, in Buddhist theory, we can train ourselves to see these unconscious movements and then leave them alone - this is in the realm of something called Vedana and is quite an illuminating field of self exploration.