How does Iago's language contribute to Othello's increasing distrust of Desdemona? How does the audience know how strong Othello's reaction is?

Some one drawing water and my theater placed my hand under the spout. as the cool stream gushed over one hand she spelled into the other the word water , first slowly , then rapidly . i stood still ,my whole attention fixed upon the motions of her fingers . suddenly i felt misty consciousness as of soothing forgotten --a thrill of returning thought and somehow the mystery of language was revealed to me this passage from the stoyof my life is an wxample of which element of plotclimax action