  We investigate small geometric configurations that furnish observable-based
proofs of the Kochen-Specker theorem. Assuming that each context consists of
the same number of observables and each observable is shared by two contexts,
it is proved that the most economical proofs are the famous Mermin-Peres square
and the Mermin pentagram featuring, respectively, $9$ and $10$ observables,
there being no proofs using less than $9$ observables. We also propose a new
proof with $14$ observables forming a `magic' heptagram. On the other hand,
some other prominent small-size finite geometries, like the Pasch configuration
and the prism, are shown not to be contextual.
