Reference for Yevamot 209:6

ואיכא דאמרי הכי שלחו ליה יבמה שרקקה תחלוץ ואינה צריכה לרוק פעם אחרת כי ההיא דאתיא לקמיה דרבי אמי הוה יתיב רבי אבא בר ממל קמיה רקקה מקמי דתחלוץ אמר ליה רבי אמי חלוץ לה ושרי לה תיגרא

cannot be mistaken;<span class="x" onmousemove="('comment',' For a proper halizah. Where the sister-in-law is allowed to marry a levir it is obvious to all who know of the recital that it was only the first formula that was recited and that no halizah had followed it. ');">¹⁴</span> spitting, however, which does not take place at the beginning but only at the end, might be mistaken [for a proper <i>halizah</i>],<span class="x" onmousemove="('comment',' Anyone witnessing the spitting would form the opinion that the other parts of the halizah ceremonial had preceded it. ');">¹⁵</span> and thus<span class="x" onmousemove="('comment',' Were she subsequently permitted to marry a levir. ');">¹⁶</span>

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