אָסוּר לֶאֱכֹל דָּג עִם בָּשָׂר, וַאֲפִלּוּ עִם שֻׁמַּן עוֹפוֹת, מִפְּנֵי הַסַּכָּנָה. וְאֵין לִצְלֹת בָּשָׂר עִם דָּג בְּתַנּוּר אֶחָד, כְּשֶׁהוּא תַנּוּר קָטָן, אֶלָּא כְּשֶׁאֶחָד מֵהֶם מְכֻסֶּה. אֲבָל בַּתַּנּוּרִים שֶׁלָּנוּ שֶׁהֵם גְּדוֹלִים אֵין לָחוּשׁ.

It is forbidden to eat fish together with meat, even with poultry fat, because it is hazardous. You should not broil meat together with fish in the same oven if the oven is small, unless either [the meat or the fish] is covered. But in our ovens which are large, you need not be concerned [and it is permissible].

כְּשֶׁאוֹכֵל דָּגִים וְאַחַר כָּךְ בָּשָׂר אוֹ לְהֵפֶךְ, יֵשׁ לֶאֱכֹל בֵּינֵיהֶם קְצָת פַּת, וְלִשְׁתֹּת אֵיזֶה מַשְׁקֶה, דַּהֲוֵי קִנּוּחַ וַהֲדָחָה.

If you eat fish followed by meat or vice versa, you should eat some bread in between and drink some beverage¹The Gemara [Mo’ed Katan 11a] writes that it is best to drink water after fish. Kesef Mishneh (Dei’os 4:18) states that nowadays people have a drink of whiskey instead. as this will cleanse and rinse [your mouth].

צָרִיךְ לִזָּהֵר מִזֵּעַת אָדָם, שֶׁכָּל זֵעַת אָדָם הוּא סַם הַמָּוֶת, חוּץ מִזֵּעַת הַפָּנִים. וְלָכֵן יִזָּהֵר שֶׁלֹּא יִתֵּן מַאֲכָל בֵּין בְּגָדָיו לִבְשָׂרוֹ מִפְנֵי הַזֵּעָה. וְכֵן לֹא יִתֵּן מָעוֹת לְתוֹךְ פִּיו, שֶׁמָּא יֵשׁ עֲלֵיהֶם מְעַט זֵעָה, וְעוֹד שֶׁיַּד הַכֹּל מְמַשְׁמְשִׁין בָּהֶן, וְיֵשׁ מֵהֶם חוֹלִים (יורה דעה סִימָן קט"ז)

You should be careful of bodily perspiration, for all bodily perspiration is poisonous except that of the face. Therefore, you should be careful not to place any food between your clothes and your body, because of the perspiration. Neither should you put coins into your mouth, for there may be some perspiration on them, and furthermore, many people handle them and there may be sick people among them.

צָרִיךְ כָּל אָדָם לִזָּהֵר תָּמִיד כְּשֶׁמֵּרִיחַ רֵיחַ אֵיזֶה מַאֲכָל, יַפְלִיט כָּל הָרֹק שֶׁבְּפִיו וְלֹא יִבְלָעֶנּוּ, כִּי אִם בּוֹלְעוֹ, יוּכַל לָבֹא לִידֵי סַכָּנָה, חַס וְשָׁלוֹם (כתובו' סא:)

When you smell the odor of food, you should spit out all the saliva in your mouth and not swallow it; for if you swallow it, it could be hazardous, God forbid.

יֵשׁ לִזָּהֵר שֶׁלֹּא לִשְׁתֹּת מַשְׁקִים שֶׁנִּתְגַּלּוּ.

Be careful not to drink water that has been left uncovered.²According to Shulchan Aruch Yoreh Deiah 116:1, this does not apply in our times because the presence of scorpions is rare. See also Orach Chaim 272 and Mishnah Berurah.

אָסוּר לִתֵּן דְּבַר מַאֲכָל אוֹ מַשְׁקִים תַּחַת הַמִּטָּה, אֲפִלּוּ הֵם מְכֻסִּים, מִפְּנֵי שֶׁרוּחַ רָעָה שׁוֹרָה עֲלֵיהֶם. ובַכְּפָרִים, יֵשׁ מַחְזִיקִים תַּפּוּחֵי אֲדָמָה וּשְׁאָר מַאֲכָלִים תַּחַת הַמִּטּוֹת, וְיֵשׁ לְהַזְהִירָם עַל זֶה.

It is forbidden to place any food or drink underneath a bed even if it is covered, because an evil spirit abides over them. In villages some people keep potatoes and other foods underneath the beds; —they should be warned against this.

וְכֵן יִזָּהֵר מִכָּל דְּבָרִים הַמְּבִיאִים לִידֵי סַכָּנָה, כִּי סַכַּנְתָּא חֲמִירָא מֵאִסּוּרָא. וְיֵשׁ לָחוּשׁ יוֹתֵר לְסָפֵק סַכָּנָה מִלִּסָפֵק אִסּוּר. וְלָכֵן אָסוּר לֵילֵךְ בְּכָל מְקוֹם סַכָּנָה, כְּגוֹן, תַּחַת קִיר נָטוּי, וְעַל גֶּשֶׁר רָעוּעַ, וְלֹא יֵצֵא יְחִידִי בַּלַּיְלָה, וְלֹא יִישַׁן יְחִידִי בַּחֶדֶר בַּלַּיְלָה. וְכֵן אָסְרוּ לִשְׁתֹּת מַיִם מִן הַנְּהָרוֹת בַּלַּיְלָה, אוֹ לְהַנִּיחַ פִּיו עַל קִלּוּחַ הַמַּיִם לִשְׁתּוֹת, שֶׁמָּא יִבְלַע אֵיזֶה דָּבָר הַמַּזִּיק (יו"ד קטן חו"מ תכז).

You should beware of all things that are hazardous because "Rules that aim to prevent danger are more strict than ritual prohibitions."³Chullin 10a. You must be more concerned with regard to a possible hazard than with a possible violation of a prohibition. It is therefore forbidden to walk in any dangerous place, such as near a leaning wall and over a delapidated bridge. You should not go out alone at night, nor should you sleep alone in a room at night.⁴If you leave the door open, or if you leave a light on, it is permitted. (She’arim Hametzuyanim Bahalachah) It is also forbidden to drink water from rivers at night, or to put your mouth into a water spout to drink, lest you swallow something harmful.

נוֹהֲגִין שֶׁבִּשְׁעַת הַתְּקוּפָה מַנִּיחִין קְצָת בַּרְזֶל עַל כָּל הַמַּשְׁקִים וּמַאֲכָלִים. וְעַל הַמְבֻשָּׁלִים אוֹ כְּבוּשִׁים אוֹ מְלוּחִים אֵין צְרִיכִין.

It is customary, at the time of the equinox⁵It seems that this custom is not observed in our time. to place a small piece of iron on all beverages and foods, but on food that is cooked or pickled, or kept in salt it is unnecessary.

אָסוּר לֶאֱכֹל מַאֲכָלִים וּמַשְׁקִים שֶׁנַּפְשׁוֹ שֶׁל אָדָם קָצָה בָּהֶם, אוֹ מִתּוֹךְ כֵּלִים מְאוּסִים שֶׁנַּפְשׁוֹ שֶׁל אָדָם קָצָה בָּהֶם, וְכֵן לֹא יֹאכַל בְּיָדַיִם מְזֹהָמוֹת. שֶׁכָּל אֵלּוּ הֵם בִּכְלַל אַל תְּשַׁקְּצוּ אֵת נַפְשׁוֹתֵיכֶם. וַאֲפִלּוּ יֹאמַר שֶׁאֵין נַפְשׁוֹ קָצָה בָּהֶם, בְּטֵלָה דַּעְתּוֹ אֵצֶל כָּל אָדָם.

You must not eat foods and beverages that are repulsive or [eat or drink] out of unclean dishes that are repulsive. Neither should you eat with dirty hands, for all these things are included [in the Biblical injunction,] "Do not make yourself repulsive."⁶Leviticus 11:43. Even if a person would say that he has no aversion to these things, his opinion is ignored since it defies the accepted norms of society.

אָסוּר לַעֲבֹר בְּנַחַל שֶׁמֵימָיו רוֹדְפִין, אִם הַמַּיִם מַגִּיעִים לְמַעְלָה מִמָּתְנַיִם, מִשּׁוּם סַכָּנָה, שֶׁלֹּא יִשְׁטְפוּהוּ הַמַּיִם (יומא דף ע"ז ע"ב)

You should not cross a stream whose waters are moving rapidly if the water reaches above the hips, for there is danger of being swept along by the current.

אָסוּר לְהוֹצִיא מִפִּיו דְּבַר פֻּרְעָנוּת עַל אָדָם מִיִשְֹרָאֵל, אֲפִלּוּ לוֹמַר, אִלּוּ הָיָה פְּלוֹנִי קַיָּם הָיָה בָּא לְכָאן, כִּי בְּרִית כְּרוּתָה לַשְּׂפָתַיִם. וְאֵין לַעֲשׂוֹת מוֹרָא לְתִינוֹק בְּדָבָר טָמֵא, כְּגוֹן לוֹמַר: חָתוּל אוֹ כֶּלֶב יִקָּחֵהוּ. וְכֵן בְּכָל כַּיּוֹצֵא בְּאֵלּוּ, צָרִיךְ לִזָּהֵר מְאֹד מֵהֶרְגֵּל הַלָּשׁוֹן (וְעַיֵּן לְקַמָּן סִימָן ר"ז סָעִיף ג').

It is forbidden to utter sinister forbodings against a fellow Jew, even just to say [about a missing person], "If so and so were alive he would have come here," for "A covenant was made with the lips."⁸The Gemara [Moed Katan 18a] explains that predictions, whether favorable or otherwise, have a way of becoming reality. When preparing to sacrifice his son, Yitzchak, on the akeidah, Abraham said to his young men; “The boy and I will go to that place … and then return to you,” (Gen. 22:5). His words came true and both did return unscathed. You should not frighten a child with an unclean thing, by saying for instance, "A cat or a dog will get you." You should be very careful [to avoid] habitual use of such similar expressions.