Decomposed housefly inside an opening Venus fly trap (Dionaea muscipula). The leaves are designed like a sophisticated mechanical trap; they are two-lobed, with a rib down the middle that functions like a hinge. The edge of each lobe has long thin spines which interlock to form a prison when the two lobes close on any unwary insect. The closure of the leaf is triggered by three long, touch- sensitive hairs on the inner surface of each lobe. When an insect is trapped, the leaf secretes an enzyme which helps to decompose it, releasing carbon & nitrogen for the plant's use.