Mistletoe (Viscum album)
Mistletoe is now quite rare and this is the first I have seen for the best part of ten years. It is a parasitic plant that grows only on standard trees. Unlike some parasites, though, it does not kill its host, just raids it for nutrients.
It has very sticky berries which birds like to eat but when they have eaten the flesh of the berry they end up with the seed stuck to their beaks. In attempt to rid themselves of it they wipe their beak on a branch, the seed comes off and a new Mistletoe plant is born.
Reproduction in nature can be so specialised you have to wonder how on earth such complex evolution came about without the plant becoming extinct in the process!