Wild rabbits get the opening case study: only one in ten survives to its first birthday, so evolution has turned does and bucks into relentless breeders, with a single mating delivering roughly three hundred million sperm and a doe ready to conceive again minutes after giving birth. From there the film moves species by species through the stranger side of animal courtship. Hippos mark territory and impress rivals by spinning their tails to fling dung in wide arcs. Melanophila beetles use infrared sensors to detect forest fires from sixty-five kilometers away, flying toward the flames to mate and lay eggs in the smoking, larvae-free wood left behind. Bowerbirds skip flashy feathers entirely and instead build and decorate elaborate structures on the forest floor, each species working in its own distinct style to catch a female's attention. Urine, dung, infrared vision, and improvised architecture all turn out to be practical tools for the same job: finding a mate and getting genes into the next generation.