The Cuckold, or "Horned Devil": A cuckold is a man whose wife has been unfaithful.  In Shakespeare's day, cuckolded men were thought to grow horns when their wives cheated on them.  Othello believes that he is a Cuckold, and becomes like a devil in personality, even though his wife has been faithful.

Animal metaphors: many animal metaphors are used in Othello. "Tupping," for one, is the copulation of sheep, and Iago uses that metaphor when talking to Brabantio about Othello and when talking to Othello about Cassio and Desdemona.  Along with the line "making the beast with two backs," these metaphors are designed to dehumanize and to elicit an emotional response.  Also, the common phrase "Croccodile Tears" comes originally from Othello. It's original meaning was "tears not cried in honesty," or "tears cried for deception."

Othello's Headaches: Othello begins to have painful headaches when he starts to believe that Desdemona has been unfaithful to him.  These headaches represent his inner pain with his feelings for Desdemona, which are of deep love, and his belief that she has been untrue. 

Fair Desdemona: Desdemona is always characterized as "fair," meaning "light-skinned." The light skin of Desdemona represents a pure body, mind, and soul as well as great beauty.  Even when Othello kills her, he cannot bear to destroy her beautiful skin, and so he suffocates her instead.