How must he warn her? [If] he said to her in the presence of two [witnesses], “Do not speak with so-and-so,” and she spoke with him —- she is still permitted to her husband, and she may eat terumah. [If] she went with him into a secluded place and stayed with him long enough to become defiled —- she is forbidden to her husband and forbidden to eat terumah; and if he dies, she must receive chalitzah and cannot be taken in yibum.