Bumblebees pollinate it by pushing their way into the tightly enclosed flowers. The seeds form in a miniature pea-pod with a beak on the end of it. They're green in my sketch (bottom left) but will turn black when ripe.
Bush vetch is a relative of the broad bean (which is doing well in our veg beds thanks to the showers we've been having). Like the bean and other members of the pea family it forms a partnership with bacteria which live in nodules on its roots. These bacteria have the ability to extract nitrogen from the atmosphere, making it available to the vetch.
The botanical name Vicia sepium is thought to derive from vincio, the Latin for 'I bind', referring to the tendrils. Sepium means 'of hedgerows'.