Here's why:

* Whiplike tail: Sperm cells have a long, whip-like tail called a flagellum that propels them towards the egg.

* Head that is almost all nucleus: The head of a sperm cell is mostly comprised of the nucleus, which contains the male's genetic material (DNA). The nucleus is so large that it takes up most of the head's space.

Let me know if you had something else in mind!