1) WHY FRUITS OF "SHEVI'IS" ARE UNLIKE OTHER ITEMS OF "HEFKER"
QUESTION: The Mishnah (50b) records an incident in which a man gave a basket of figs of Shevi'is to five women, two of whom were sisters, for the sake of Kidushin. The Chachamim ruled that none of the women are Mekudeshes. The Gemara cites Rav who infers from the Mishnah that in an ordinary case of Kidushin (when a man is Mekadesh one woman) with fruits of Shevi'is, the Kidushin takes effect.
RASHI gives two explanations for Rav's statement. The first explanation is that Rav is teaching that although the fruits are fruits of Shevi'is, they nevertheless are considered the man's monetary possession and thus he may be Mekadesh a woman with them. Although the Torah states that fruits of Shevi'is are Hefker (ownerless), since the man picked them up and acquired them they become his monetary possession for all purposes. The second explanation is that Rav is teaching that one should not assume that fruits of Shevi'is may not be used for any purpose other than normal consumption (i.e. eating); rather, they may be used even for unusual purposes, such as Kidushin.
According to the first explanation of Rashi, why would one have thought that the man should not be entitled to perform Kidushin with fruits of Shevi'is? Why should such fruits differ from any other item of Hefker that becomes the property of the person who picks it up, who acquires it and may use it for any purpose he wants?
ANSWER: The PNEI YEHOSHUA explains that one might have thought that fruits of Shevi'is contain such a high degree of Kedushah that they are like Ma'aser Sheni which, according to some Tana'im, is considered "Mamon Hekdesh" (the property of Hekdesh) and may not be used for Kidushin (since the man is not the owner). Indeed, the Gemara later (53a) entertains the possibility that fruits of Shevi'is may have such Kedushah. Therefore, the Gemara here teaches that once a person has picked up and acquired the fruits of Shevi'is, they are considered "Mamon Hedyot" (owned by man) and they may be used for Kidushin.
2) A WOMAN WHO SINS WHILE ACTING AS A "SHALI'ACH" FOR KIDUSHIN
QUESTION: Rav infers from the Mishnah (50b; see previous Insight) that a man may be Mekadesh a woman with fruits of Shevi'is. RASHI explains (in his second explanation) that the prohibition of conducting business (Sechorah) with fruits of Shevi'is does not apply to using the fruits to be Mekadesh a woman. TOSFOS (DH ha'Mekadesh) disagrees and maintains that the prohibition of Sechorah applies in such a case, but the Kidushin is valid since the prohibition is only l'Chatchilah and does not stop the Kidushin from taking effect b'Di'eved. (According to Tosfos, this is the Chidush of the Mishnah.)
However, the Mishnah seems to disprove the explanation of Tosfos. In the case of the Mishnah, one woman acted as a Shali'ach on behalf of the other women and accepted the fruits of Shevi'is for them. According to Tosfos, who maintains that the prohibition of Sechorah applies to an act of Kidushin with the fruits of Shevi'is, the woman's Shelichus to receive the fruits for the other women should be considered a "Shelichus l'Devar Aveirah" and should not be valid at all. Although Kidushin performed with fruits of Shevi'is takes effect b'Di'eved, the act done by a Shali'ach should not be valid at all, since a Shali'ach cannot be appointed to transgress a Torah prohibition. The Shelichus should be annulled and the Kidushin should not take effect for any of the women other than the woman who accepts the fruits for himself.
ANSWERS:
(a) The SEFER HA'MIKNAH answers that the principle of "Ein Shali'ach l'Devar Aveirah" applies only when the Shali'ach is specifically appointed to transgress the Aveirah. When the Shali'ach was not appointed specifically to transgress the Aveirah, but it merely happened that the Shali'ach transgressed, the principle of "Ein Shali'ach l'Devar Aveirah" does not apply.
In the case of the Mishnah, the other women did not instruct the Shali'ach to transgress an Aveirah and accept fruits of Shevi'is for Kidushin. They simply instructed her to accept money, or an object of value, for the sake of Kidushin. When the Shali'ach accepted from the man fruits of Shevi'is for the sake of Kidushin, she acted on her own volition and not as the representative of those who sent her. Hence, the Aveirah is not an inherent part of the Shelichus and the Shelichus is not considered a "Shelichus l'Devar Aveirah." (See KETZOS HA'CHOSHEN 182:2.)
(b) The NODA B'YEHUDAH offers a different explanation. He explains that when the man gives fruits of Shevi'is to the woman for Kidushin, it is the man, and not the woman, who transgresses the prohibition of Sechorah with fruits of Shevi'is, because he is the one who performs the act of Kidushin. The woman who accepts the Kidushin is a Shali'ach of the other women and not of the man. Since her act of accepting the Kidushin involves no Aveirah, the Shelichus remains valid and the Kidushin takes effect.

52b----------------------------------------52b

3) WASHING ONE'S FEET AT THE MOMENT OF MARRIAGE
QUESTION: The Gemara relates an incident in which a man snatched money from his friend and then gave it as Kidushin to a woman who was washing her feet in a bucket of water. Rava ruled that the Kidushin is not valid because the Halachah does not follow the view of Rebbi Shimon who rules that in a normal case of theft the victim despairs of ever recovering his money ("Ye'ush"). Rather, the victim does expect to recover his money and thus the thief did not acquire the money (with a Kinyan of Gezeilah) for himself.
The Gemara's intention is to teach that in a normal case of theft the owner does not despair of retrieving his property. Why does the Gemara mention the seemingly unrelated detail that the woman happened to be washing her feet at the moment of the Kidushin?
ANSWER: The RITVA explains that one might have thought that when a woman is in the midst of grooming herself, she does not pay attention to her surroundings. When the man said to her, "You are hereby betrothed to me," the woman did not respond. One might have assumed that she was so involved with grooming herself that she did not pay attention to what he said, and that is why the Kidushin was not valid. The Gemara therefore teaches that the only reason why the Kidushin was not valid is that the Kidushin was performed with stolen money. Had the Kidushin been performed with the man's own money, the Kidushin would have taken effect even though the woman did not respond to his statement of betrothal. Her silence would have been construed as consent to the marriage.