Flirting is not restricted to humans; it has many parallels in the animal world, seen in the behavioral displays many animals engage in to signal their availability and suitability. Animal courtship varies tremendously between species, ranging from subtle movements to lavish displays. For example, penguins search for pebbles to deliver to their partner of interest. Seahorses lock their tails together for a romantic swim. Bower birds use leaves, grass, and twigs to construct elaborate nests.