In the second installment of the documentary Tierra Envenenada -- "The Poisoned Land" -- we open with instructions given to children. The instructions are meant to teach them to look out for signs of danger. Do you know the internationally recognized icon of danger?
¿Qué figura es esa?
What figure is that?
Una calavera, una calavera, una calavera...
It's a skull, a skull, a skull...
Captions 8-9, Tierra Envenenada - Desminando - Part 2Play Caption
The spooky image of the skull, spoken by the young boy in the documentary is repeated above for effect. Aside from being an icon of danger, many of us also know the skull as a ubiquitous symbol of Mexico's Día de los Muertos, as well as rock & rollers everywhere.
If you want to be medically technical, you might use cráneo to say "skull" in Spanish, but that's more like saying "cranium" in English. Yes, it's the bone structure of the head, but it's not as symbolically evocative.
Slang lovers will note that calavera can also mean "daredevil" or "madcap" -- as in "un hombre calavera." However, that is far from the lesson this serious documentary about the danger of land mines seeks to impart.