In the Selva Oscura, the Leopard, the Lion, and the She-Wolf block the pilgrim from following the straight path and force him to retreat deeper into the Dark Wood of sin. The beasts are so ferocious even their growls make the air tremble with fear. There is much debate among Danteists and scholars about what the three beasts represent. Some associate them respectively with Fraud, Violence, and Concupiscence or Envy, Pride, and Avarice. Others believe that they have some sort of political meaning or represent the three divisions of hell. Although it is unclear what they represent, it is obvious that they fill the pilgrim’s heart with unspeakable terror. 
Upon their arrival in hell, the damned confess their sins to a large growling beast named Minos who determines in which circle of the Inferno they will spend eternity. The number of times he coils his tail around himself is equal to the circle of hell to which the damned soul must descend. Dante bases Minos on the Classical Greek Mythological figure of the same name. Minos was the Ruler of Crete, the son of Zeus and Europa, and in the Underworld, served as the judge of the dead. 
In classical mythology a ferocious three-headed dog named Cerberus guards the Underworld. In the Inferno, Dante assigns him the role of guardian of the Gluttons in the third circle of hell. He has red eyes, a swollen belly, and tears at the gluttons with his monstrous fangs and claws. Dante describes him as a filthy creature with three voracious throats. Virgil attempts to quiet the beast by throwing him large fistfuls of muck and slime that he devours with his three hungry mouths. 
Li occhi ha vermigli, la barba unta e atra,
e 'l ventre largo, e unghiate le mani;
graffia li spiriti ed iscoia ed isquatra. (Inf. XI. 16-18)
Virgil and Dante's descent into the ninth and final circle of hell is one of the most terrifying moments of the Inferno and is brilliantly captured by Botticelli, Doré, and Flaxman in their illustrations. In this scene, Dante sees Satan, immersed in a giant lake of ice. Brutus, Cassius, and Judas, the most notorious traitors in history, dangle from each of Lucifer's three mouths. Brutus and Cassius plotted against, betrayed, and assassinated Julius Caesar, the ruler of the Roman Empire from 49 to 44 BC. Judas Iscariot, a disciple of Jesus, betrayed his Savior for thirty pieces of silver. 
A Minotaur, or a creature half man and half bull, guards the Violent of the seventh circle of the Inferno. The beast tries to block Dante and Virgil from entering the circle, and so Virgil taunts him. The Minotaur goes into a rage and Dante and Virgil scurry past him.  The poets make their way to a river of boiling blood in which the violent are immersed. They see a group of Centaurs, or beasts who are half-man and half-horse, guarding the riverbank. They shoot arrows at those attempting to rise out of the boiling water. Nessus, one of the Centaurs, guides Virgil and Dante across the river. 
Geryon is a winged creature representing Fraud. He has a human face, the paws of a lion, and a long tail. He transports Virgil and Dante into the eighth circle of the Inferno. 
Virgil and Dante continue in their journey and come across a strange forest guarded by half-bird, half-woman creatures called harpies. They shriek and are perched upon trees with twisted branches. Instead of fruit or green leaves, the trees bloom poisoned thorns. When Dante breaks off a tiny branch from one the trees, the tree begins to bleed. He hears a voice cry out: "…Why do you rip me?/ Have you no sense of pity whatsoever?"  The voice is Pier della Vigna, the former counselor of Frederick II of Sicily. Pier was Fredrick’s faithful servant and was falsely accused by his political enemies of plotting against him. In prison, Pier committed suicide and descended to the Wood of Suicides in the seventh circle of hell. 
1. Selva Oscura. Inf. I-II.
2. Minos. Inf. V.
3. Cerberus. Inf. VI.
4. Lucifer. Inf. XXXIII-XXXIV.
5. Minotaurs. Inf. XII.
6. Centaurs. Inf. XII.
7. Geryon. Inf. XVII.
8. Citation. Inf. XIII. 35-36. Dante Alighieri, and Mark Musa. Dante Alighieri's Divine Comedy. Bloomington: Indiana University Press, 1996.
9. Harpies and the Wood of Suicides. Inf. XIII.
10. Raffa, Guy P. The Complete Danteworlds: A Reader's Guide to the Divine Comedy. Chicago ; London: University of Chicago Press, 2009.