The snake and knife tattoo shows that life is a constant fight or battle. It dates back to Irish traditions and shows that there is a constant cycle of fighting in a person's life.
The knife in the tattoo is a symbol for a fight. A fight that is being fought internally, a fight that has been fought physically or any metaphorical meaning for a fight. It is a symbol that has been used for centuries in Irish tradition because a modern day knife is similar to an ancient dagger, which was only used during fights. The snake in the tattoo is a symbol of a constant or a cycle in someone's life because the snake stands for renewal and cycling through something. The combination of these two symbols literally means to live by constantly fighting.