Explain Emilia’s and Iago’s response in the discussion with Desdemona about Othello’s name calling (Desdemona can’t even repeat the phrase)

Emilia is irate at Othello for calling her Desdemona a " whore ",

"Alas, Iago, my lord hath so bewhored her,

Thrown such despite and heavy terms upon her,

That true hearts cannot bear it."

Iago merely pretends to be angry,

"Beshrew him for ’t!

How comes this trick upon him?"