The snake

In Christian iconography it is one of the most important and most complex symbolic animals.  Genesis says that the snake is the most astute of the wild animals that God made and tempted Adam and Eve in the episode of the original sin. It then became the symbol of the demon, the enemy of God, and appears wrapped around the Tree of Life, in the form of an ascending spiral, that is interpreted as a rebellion against God.  In the pillar of Camarasa and the paintings of Sixena you can see the representation of the original sin, with Adam and Eve on each side of the Tree of Life and the snake wound round the trunk.  They said it fled from the naked man and only attacked if he was dressed.  For this reason, while Adam went naked through Paradise the snake didn't dare attack him, because he was clean of sin, but when he was dressed of mortality and was covered with vices, it jumped on him. 
Despite its harmful and negative symbolism (protagonist of the original sin, representation of the demon and figuration of hell and personification of evil in the Final Judgement), at times it makes reference to Christ and acquires a more positive sense.