"We must not buy their fruits:
Who knows upon what soil they fed
Their hungry thirsty roots?'..."
See in text (Goblin Market )
This powerful metaphor for evil is one of the most quoted lines from this poem. "Hungry thirsty roots" and "fed" suggest overconsumption. In speculating "what" these fruits were eating, Lizzie suggests that they were indulging in something evil or suspect. This metaphor underscores a larger theme within the poem: that which one eats defines them and can taint them forever.