This is a very simple addon that helps keep you finishing a nice hard night of raiding just to wonder why your mana never seemed to drop and you got out DPSed by that priest's improved Power Word: Shield.
When your mana is full, you get told to turn off Aspect of the Viper. When your mana is empty, you get told to turn it on.
Configuration is done via the options panel; there is no command line interface. You can change the text that is displayed, add sound effects, and modify the percentage of mana at which you get warnings.
If you are not a hunter, it does nothing at all.