The frog has a number of vices in the poem "The Frog and the Nightingale" by Vikram Shrath. He is arrogant, egocentric, money hungry, and takes advantage of other. The nightingale is humble but naive.
First of all, the frog is self-centered and arrogant. This is clear when he croaks on and on in the bog, even when all the other animals try to get him to stop as is evidenced by these lines:
Neither stones nor prayers nor sticks.
Insults or complaints or bricks
Stilled the frogs determination
To display his heart's elation.
The frog also boasts of his "splendid baritone" to the nightingale as she prepares to sing the next night. Possibly out of jealousy or from a desire to make money, the frog trains the nightingale and then profits from her voice. Making a profit is not necessarily a vice, but the way that he convinces the very naive nightingale that he is an expert smacks of deception.
The nightingale lacks self-confidence. Initially, she appears merely humble, clearly a virtue, stating that she "doesn't think the song's divine" but at least it is hers. However, that humility transforms into naivety when she is taken in by the frog's boasting and is duped. Instead of leaving the frog, she stays growing more and more depressed which eventually leads to her death. The nightingale's choice to stay could be viewed as a vice as she lacked the willingness to stand up for herself.
The frog's egocentrism is more and more apparent as the poem progresses. He charges her a small fee for training, exploits her voice for his profit by charging for performances, starts her training when it is raining, weather hardly good for the bird's health. When she dies, he blames the nightingale, calling her "stupid", "nervous", and "far too prone to influence."