In late spring, a pair of white flowers (with a single calyx) appears. Each small, fragrant flower has four brilliant white petals that are pubescent and unite into a funnel-shaped tube that is also fringed with hairs. The pair of flowers occur in two forms (dimorphous). In the first form the pistil is short and the stamens are long; in the second form the pistil is long and the stamens are short. This structure prevents each flower from fertilizing itself. Both flowers must be pollinated to obtain a single scarlet berry. Each berry is the result of the fusion of each ovary of the pollinated pair of white flowers. As such, each berry has two bright red spots on its surface.
(quoted from USDA site)