Throughout the play, as Othello's fear and anger increase, he reveals himself more and more to be manipulated by Iago. This is partly shown by the manner in which Othello expresses his suspicions, but also, in some instances, Iago's specific wording which Othello echoes, as when he says to Emilia:
Cassio did top her, ask thy husband else.
Iago sees men and women in animal-like terms. Early in the play he describes two people making love as "the beast with two backs." In general, his language is filled with crude allusions and obscenities. Othello is increasingly influenced not only into believing Desdemona has been unfaithful, but into using the cynical, cruel style of speech in which Iago revels. "A horned man's a monster and a beast," Othello says, referring to the proverbial "horns" of a cuckolded man. He also has accepted the division between himself and the Europeans that Iago has exploited. "Do ye triumph, Roman?" Othello asks, indirectly addressing Cassio. Othello becomes increasingly brutal, saying he will "throw Cassio's nose" to a dog, and then finally striking Desdemona in front of the others. It's as if Iago has taken over Othello's personality and possessed Othello's soul.
An interesting point, in this connection, is that Iago's destruction of Othello is motivated by jealousy. Though Iago hates Othello, he's ironically making Othello into a kind of mental twin of himself, full of anger and hatred. It's a sick, psychotic kind of bonding Iago imposes on Othello. What seems equally tragic with the murder of Desdemona and Othello's suicide is Othello's inability to deal Iago a fatal blow. He runs at him with a sword but only wounds Iago, who "bleeds [but is] not killed." It's as if Othello has become powerless against Iago because Iago has so fully controlled his spirit.