אורח חיים צ״זOrach Chayim 97

Se’if 1א׳

לֹא יְגַהֵק (מוֹצִיא מִגּוּפוֹ לְפִיו נְפִיחָה מִתּוֹךְ שָׂבְעוֹ רייטי"ר בְּלַעַ"ז), וְלֹא יְפַהֵק (חֵיךְ מָלִקוֹחָיו פּוֹתֵחַ פִּיו לְהוֹצִיא רוּחַ הַפֶּה); וְאִם צָרִיךְ לְפַהֵק מִתּוֹךְ אֹנֶס, יַנִּיחַ יָדוֹ עַל פִּיו, שֶׁלֹּא תֵּרָאֶה פְּתִיחָתוֹ. וְיִזָּהֵר שֶׁלֹּא יַנִּיחַ יָדוֹ עַל סַנְטְרוֹ בִּשְׁעַת הַתְּפִלָּה, דְּהָוֵי דֶּרֶךְ גַּסּוּת הָרוּחַ, (טוּר וְהָרִי"ף).

One Should Not Belch or Yawn During the Prayers, containing 5 s'ifim One should not belch (i.e. one brings out from his body to his mouth, a blowing, as a result of one's satiation - "ritiur" in Old French) nor yawn (i.e. the palate of one's jaws opens to bring forth a breath from the mouth). And if one needs to yawn due to a compulsion, one should place one's hand over one's mouth so that its opening will not be seen. And one should be careful to not place one's hand on one's chin during prayer, for that is the way of haughtiness (Tur and the Ri"f).

Se’if 2ב׳

אָסוּר לוֹ לָרֹק; וְאִם אִי אֶפְשָׁר לוֹ שֶׁלֹּא לָרֹק, מַבְלִיעוֹ בִּכְסוּתוֹ בְּעִנְיָן שֶׁלֹּא יְהֵא נִרְאֶה; וְאִם הוּא אִסְטְנִיס, (פי' שֶׁאֵינוֹ יָכוֹל לִרְאוֹת דְּבַר מִאוּס), וְאֵינוֹ יָכוֹל לְהַבְלִיעוֹ בִּכְסוּתוֹ, זוֹרְקוֹ לַאֲחוֹרָיו. וְאִם אִי אֶפְשָׁר לְזָרְקוֹ לַאֲחוֹרָיו, זוֹרְקוֹ לִשְׂמֹאלוֹ, אֲבָל לֹא לִימִינוֹ; וְכָל שֶׁכֵּן לְפָנָיו, דְּאָסוּר, (הר"י פ' מִי שֶׁמֵּתוֹ). (וְהָא דִּלְקַמָּן בְּרֵישׁ סי' קכ"ג שֶׁהוֹפֵךְ פָּנָיו לְצַד שְׂמֹאלוֹ תְּחִלָּה, שֶׁהוּא יָמִין שֶׁל הָקָבָּ"ה, י"ל הַטַּעַם כֵּיוָן שֶׁמֵּעוֹלָם לֹא יָרְדָה הַשְּׁכִינָה לְמַטָּה מי' אִם כֵּן אֵין הַשְּׁכִינָה כְּנֶגֶד הַמִּתְפַּלֵּל, וּלְפִיכָךְ חָלְקוּ כָּבוֹד לְיָמִין דִּידֵיהּ בִּרְקִיקָה שֶׁהִיא בִּשְׁעַת תְּפִלָּה אֲבָל כְּשֶׁפּוֹסֵעַ שְׁלֹשָׁה פְּסִיעוֹת, הָאָדָם מַרְחִיק עַצְמוֹ מִמְּקוֹם תְּפִלָּתוֹ וְהוּא כְּנֶגֶד הַשְּׁכִינָה, וּלְפִיכָךְ נוֹתֵן שָׁלוֹם לִשְׂמֹאלוֹ שֶׁאָז הוּא כְּנֶגֶד יְמִינוֹ שֶׁל הָקָבָּ"ה) (בֵּית יוֹסֵף בְּשֵׁם אָבִיו).

It is forbidden for one to spit [while praying the Amidah], and if it is impossible for one not to spit, one should absorb into one's clothing in such a way that it is not visible. And if one is sensitive [i.e. one cannot stand to see something disgusting] and one is not able to absorb it into one's clothing, one should cast it behind oneself. And if it's impossible to cast it behind oneself, one should cast it to one's left, but not to one's right and all the more so, in front of one is prohibited [Rabbeinu Yonah - (Tractate Berachot - Chapter 3) "Mi Shemeito"]. And this that [it says] below at the beginning of Orach Chayim 123, that [when taking 3 steps back at the end of the Amidah] one turns one's face to the left side first because that is the right [side] of the Holy One Blessed Be He [who is opposite one], it is possible to say the reason is since the Shekhina [the Indwelling Presence of Hashem] never goes below 10 [handbreadths], and if so, the Shekhina is not directly in front of the one praying, and therefore, they gave honor to the right [side] of the person in [regards to] spitting at the time of praying. But when stepping 3 steps back, the person is distancing oneself from the place of his prayers, and now one is opposite the Shekhina, and therefore he gives "Shalom" (i.e. one says the words "Oseh Shalom Bimromav" - "He who makes peace up above") to one's left, for then it is opposite the right of the Holy One Blessed Be He [Beit Yosef in the name of his father].

Se’if 3ג׳

אִם כִּנָּה עוֹקַצְתּוֹ, יְמַשְׁמֵשׁ בִּבְגָדָיו לַהֲסִירָהּ שֶׁלֹּא תִּתְבַּטֵּל כַּוָּנָתוֹ, אֲבָל לֹא יְסִירֶנָּה בְּיָדוֹ. הַגָּה: וְדַוְקָא בִּשְׁעַת הַתְּפִלָּה, אֲבָל שֶׁלֹּא בִּשְׁעַת הַתְּפִלָּה יָכוֹל לִטֹּל כִּנָּה וּלְזָרְקוֹ בְּבֵית הַכְּנֶסֶת (אוֹר זָרוּעַ), וְעַיִּןִ לְעֵיל סי' ד' סָעִיף י"ח.

If a louse bites [a person in the middle of praying the Amidah], one should use one's garment to remove it so that one will not lose one's concentration, but one should not remove it with one's hand. Gloss: And this is specifically at the time of the prayer [i.e. Amidah], but when not at the time of the prayer [i.e. Amidah], one may take the louse [with one's hand] and to throw it away in the synagogue [Ohr Zarua]. And see above in Orach Chayim 4:18.