From Awake, My Glory, by Rabbi Avigdor Miller
The pitcher-plant exudes a sweet odor to lure insects into its hollow.
The down-pointing spikes prevent the insects from escaping from the hollow.
The pool at the bottom of the hollow drowns the insects. The digestive enzymes in the pool digest the prey.
Thus the odor and the spikes and the pool and the enzymes are all essential for the nourishment of the plant, and they all collaborate for one end-purpose.
Click for larger images; Wikipedia, Commons