‘The Green Lion Devouring The Sun’ is a popular alchemical symbol. On a chemical level this is a metaphor for when a green, liquid sulfate called “vitriol” purifies matter, leaving behind the gold within the matter. Very pure vitriol is an acid that eats through practically anything, except gold.
On a human level, it's a metaphor for when a person’s “consciousness [is] overwhelmed by violent, frustrated desires”. In other words, inside a person, when the metaphor takes place, the person is compelled to act out destructively.
In contrast; the person can allow the ‘green lion’ to eat them in order to be purified — to become spiritually golden.