Who says this? What does it mean? " I know our country disposition well;/ in Venice they do let heaven see the pranks/They dare not show their husbands; Their best conscience/ Is not to leave't undone, but keep't unknown.

Iago says this to Othello. Here he is cultivating the seeds of doubt in Othello's mind. Iago says he knows people in this country do bad things. They really don't want to get caught but one can see their sins if they look closely. Iago wants Othello to watch his wife.