*Two backs actually.
Pretty much the openning scene in the play when they senator guy is talking with the two guards. Shakespeare suggests a great deal of beastiality when talking about the Othello. Such as:
Beast with two backs
That line where they describe the type of children Othello and Desdemona will have:
When the guards tell them to go and look for him at the Saggitary. (Sagittarius is iconoclased by a centaur - a half-man half-beast creature.
So basically your last paragraph could describe them methods in which Shakespeare attributes beastiality to Othello's race.
There are loads of others if you look for them. I just thought these were the most prominent.