It is customary before the groom gives the ring (or coin) to the bride under the Hupa for the Rav Ha’mesader (officiating Rabbi) to turn to the witnesses, show them the ring, and ask whether the ring in their estimation is "Shava Peruta" (worth the value of a simple coin). The witnesses then answer in the affirmative.
This custom is mentioned by the Rama (Rabbi Moshe Isserles, Cracow, 1525-1572), in Eben Ha’ezer (31:2). The reason for this practice, as explained by the Helkat Mehokek (commentary to Eben Ha’ezer by Rav Moshe Lima, Poland, 1604-1658), is that the woman might otherwise have misconceptions about the ring’s value. She might be under the wrong impression that it is worth many thousands of dollars, and if so, when she later discovers that it is worth much less, she might have regrets which could call into question the validity of the Kiddushin. The Rabbi therefore has the witnesses affirm in her presence that the ring is worth at least a "Peruta," but not necessarily more than that, in order to dispel any possible misconceptions.
In light of this reason, it is important that the woman hears the witnesses’ confirmation about the value of the ring. If the Rabbi’s back is turned to the bride as he speaks to the witnesses, and they answer him without the bride hearing, then this brief conversation is meaningless. Since the entire purpose is for the bride not to harbor expectations about the ring’s value, she needs to hear the witnesses’ say that the ring is "Shava Peruta." Thus, the Rabbi and witnesses must ensure to have this exchange in view of the bride in a manner that she is able to hear them. Furthermore, she must understand what they are saying. If she does not understand the terms, the Rabbi and witnesses must fully explain what they are saying, so she understands full well that they are affirming that the value of the coin is a "Shava Peruta," and is not necessarily worth any more than that.
Additionally, the witnesses should simply respond, "Yes," without any comical remarks. Some witnesses might jokingly respond to the Rabbi’s question whether the coin is worth a "Shava Peruta" by saying, "Oh, and how!" Such a response would, of course, defeat the entire purpose of this exchange, which is to dispel any possible misconceptions that the ring is worth a lot of money. It is therefore important for the witnesses to simply answer "Yes" without saying anything else.
Summary: Before the groom gives the ring to the bride, the Rabbi shows it to the witnesses and asks them if it is "Shava Peruta," to which they answer, "Yes." This is done so that the bride would not mistakenly think that it is very expensive. The bride must therefore hear and understand this brief exchange. The witnesses should simply respond "Yes" without adding any humorous remarks.
