Why do we want the things we want? What really drives us? And how in control of our instincts are we? All questions you might ask the humble cuckoo. This dastardly bird - a 'brood parasite' - famously leaves its eggs in another bird's nest and flies off, never to be seen again. The enormous chick hatches, kills all its nest-mates, then runs its adoptive parents ragged with round-the-clock feedings. But why on earth do the poor host-parents fall for the con? To find the answer, Becky Ripley and Emily Knight delve into the history of animal behavioural research to uncover the 'Supernormal Stimulus', a curious phenomenon in which an animal's most basic instincts can be over-ridden, twisted and manipulated, to make them behave in extraordinary ways. Often against their own best interests. And if you think humans are far too smart to be manipulated in this way, think again. Take a look at the things you like, and ask yourself why? Why do you like fast food when it's so bad for you? Why is porn so appealing, when it's so unrealistic? And why can't you put your smart-phone down? Perhaps just like the parasitised victims of the cuckoo chicks, you're not completely in control of what you want. Featuring evolutionary biologist professor Rebecca Kilner and evolutionary psychologist Becky Burch