Chapter 33: 4-7
Matter Forbidden Due to Danger
4. Everyone should be careful to spit out all the saliva in his mouth that
collected when he smelled the aroma of foods. It should not be swallowed,
lest it cause danger, Heaven forbid (Kesubos 61a).
5. A person should take care not to drink liquids that have been left open.
6. It is forbidden to place any food or drink under a bed, even though it
is covered, because the spirit of impurity [that rests on a person while he
sleeps (see Chapter 2)] rests on them as well. In the outlying villages,
people are accustomed to keep potatoes and other foods under their beds;
and they must be advised about this.
7. A person should take great care regarding all dangerous matters.
[Chullin 10a] teaches: "The regulations instituted because of possible
danger are stricter than prohibitions."
Accordingly, it is forbidden to walk in a dangerous place - for
example, under a leaning wall or on a shaky bridge. A person should not go
out alone at night, nor should he sleep alone in a room at night.
Similarly, it is forbidden to drink water from the rivers at night or to
place one's mouth under a flow of water to drink, lest one swallow [a leech
or] something else harmful.