Yes, many Lego minifigures and pieces only are produced in one set, sometimes discontinued, making them very rare.
no there has been many rumours but Lego said there is no plans for a Lego halo game
Lego makes about that many a year there have been about 500 or more.
2
a lot
There are billions of Lego in the world, and each person is equivalent to 60 Lego bricks!
a trillion
yes there has been many case's where snakes has been born with 2 heads
There Are Many Lego Men but not many Lego Women
Twelve Star Wars Lego Sets have been produced for seven series of Star Wars show. The seven series of the Star Wars show mentioned are The Phantom Menace, Attack of The Clones, Revenge of The Sith, A New Hope, The Empire Strikes Back, Return of the Jedi and The Clone Wars.
4 cells have been produced at the end of meiosis
5