Aside from its depiction of a charming-but-homicidal AI, 2001: A Space Odyssey is perhaps best remembered for its monoliths. Seemingly out of nowhere, these perfectly smooth and space-black slabs compel prehistoric apes—and later, an advanced team of astronauts—forward to touch and understand them. To see into whatever secrets they might contain. The film stays purposely ambiguous about the meaning of these monoliths.