The day before the festival of Shiva (on February 20), I came across one of his devotees with his trident (!!) while waiting for my rickshaw:
In the evening, during dinner, I asked my hosts: “What is Maha Shivatri?”.
Answer of the father: “no idea”.
Answer of the mother (who thought hard): “Once upon a time there was Vishnu who spent much of his time lying down on his snake itself lying on the ocean. One day the ocean was irritated and started to throw up things. The demons and the gods shared them but nobody wanted the poison. Then Shiva sacrificed himself and swallowed the poison. But his wife, refusing him to die, put her hands around his neck so that the poison would not go down. But the gods, refusing the poison to be spelled out, blocked his mouth. Thus the poison remained in Shiva’s head and that it is why he is blue. This is what we celebrate for Maha Shivaratri.”
Apparently it is the right explanation (at least one of the right explanations)! http://hinduism.about.com/od/festivalsholidays/p/mahashivratri.htm