Song of Songs 1:9:
I liken you, my darling, to a mare
among Pharaoh’s chariot horses.
In this verse the speaker draws a comparison between two things: his beloved and a mare harnessed to a chariot of Pharoah. The difference between the two objects in the comparison draws our attention and set us thinking. The next step is to identify the comparison. In this particular case, some historical background is necessary to understand the impact of the compliment. Research makes it clear that the chariots of Egypt used stallions, not mares. The presence of a mare would sexually excite the stallions. Pope points out in his commentary (1977, 336-41) that Israel knew of a battle tactic that called for the release of a mare among the enemy’s chariot horses to divert their attention.
-from Longman and Dillard, An Introduction to the Old Testament (Zondervan 2d Ed. 2006), at page 28, where the authors discuss biblical imagery.
The commentary to which they refer is Marvin H. Pope, Song of Songs: a New Translation with Introdution and Commentary (The Anchor Bible 1966).