Chullin 106 - Washing One's Hands
Washing the hands before the meal is a mitzvah, but washing them afterwards is an obligation, because of the dangerous salt that may be present on the hands. The first water may be warm, but the last water must be cold.
Two porters once carried a barrel of wine and stopped to rest, placing the barrel under a drainpipe. The invisible demon frequently found under a drainpipe caused the barrel to burst. The porters sued the demon in the court of Mar bar Rav Ashi. At first the demon refused to come, but Mar, adept at practical kabbalah, forced him with shofar blowing, and he appeared. Mar asked, "Why did you break the barrel?" The demon answered, "What was I to do, when they placed the barrel on my ear as I was sleeping." However, Mar told him, "Since you slept in a public place, you are the one who acted irregularly, and you have to pay." The demon asked for some time, and avoided the payment in the end.
It once happened that someone did not wash his hands before the meal, was taken for a non-Jew, and was fed pork as a result.
Art: Mikhail Aleksandrovich Vrubel : Demon sitting