A most unusual use of illusion on a coin. The two confronting boars' heads can also be viewed as the facing head of a panther.
Silver 1/10th stater, SGCV II 3488, Rosen 542, F, 1.208g, 9.9mm, Lesbos mint, c. 500 - 450 B.C.; obverse confronting boar heads, creating the illusion of a facing head of a panther; reverse incuse square punch. RARE.