Clues may arise from common practice, characteristic properties, or the local context. Rest and livelihood invite familiar night/day associations; a gazelle and the eyes are linked by a conventional poetic comparison.
A semantic clue is not contrary to the figure; it is what allows the listener to restore the second set to the first. But if a predicate fits several referents equally well and nothing favors the intended matching, the expression no longer yields a clear example.
The rhetorical achievement is therefore not obscurity for its own sake but economy that involves the reader in recovering a determinate meaning.