FORBIDDING SOMETHING NOT YET IN THE WORLD [line 1]
Answer #1 (R. Ila): We find this regarding one who says 'this field that I sell to you should be Hekdesh when I buy it back!'
Objection (R. Yirmiyah): The comparison is faulty! There, he can be Makdish it now (before selling it). A woman cannot divorce herself!
Our case resembles one who says 'this field that I sold to you should be Hekdesh when I buy it back.' It does not become Hekdesh!
Objection (Rav Papa): The comparison is faulty! There, the buyer owns the field itself and its produce. Here, the wife owns her hands!
Answer #2 (Rav Papa): We find Hekdesh that cannot take effect now, but takes effect later regarding one who says 'this field that I mortgaged to you (gave for collateral for a loan, to eat its fruit until the loan is repaid) should be Hekdesh when I redeem it.' The field becomes Hekdesh!
Objection (Rav Shisha brei d'Rav Idi): The comparison is faulty!
There, he can redeem the field. A woman cannot divorce herself!
Answer #3 (Rav Shisha brei d'Rav Idi): We find this when one says 'this field that I mortgaged to you for 10 years should be Hekdesh when I redeem it.' The field becomes Hekdesh!
Objection (Rav Ashi): The comparison is faulty! There, he can redeem the field after 10 years. A wife can never divorce herself!
Answer #2 (to Question 2:i, 85b - Rav Ashi): One cannot ask a question from Konamos. They are different. They are like Kedushas ha'Guf (something used for Avodas ha'Mikdash), like Rava taught:
(Rava): Hekdesh (ha'Guf), the Isur of Chametz, and freeing a slave uproot liens.
Question: If so, her earnings should become forbidden immediately. Why does the Mishnah say that the concern is lest he divorce her?
Answer: Really, her earnings are forbidden immediately. The Mishnah says 'lest he divorce her' to teach that even if it does not become Hekdesh now (because Chachamim strengthened the lien of a husband), still, he should annul the vow.
MISTAKEN ANNULMENT [line 5]
(Mishnah): In the following cases, a man can go back and annul a vow after he learns of his mistake. (If he already affirmed or annulled it, this was invalid):
His wife vowed, and he thought that his daughter vowed, or vice-versa;
She vowed to bring a Korban, and he thought that she vowed to be a Nezirah, or vice-versa;
She vowed from figs, and he thought that she vowed from grapes, or vice-versa.
(Gemara) Inference: "He will annul her" teaches that he must know whose vow he annuls!