Answer:
In Victor Hugo's "The Hunchback of Notre-Dame," Quasimodo believes he is not a bird due to his acute awareness of his severe physical deformities and the stark contrast between his own grotesque appearance and the beauty, grace, and freedom associated with birds. His hunched back, misshapen head, and solitary eye make him profoundly different from the sleek, aerodynamic form of birds. This perception is reinforced by the way others treat him with fear and mockery, solidifying his sense of being earth-bound and imprisoned by his physical and societal constraints. Additionally, his deep connection to the stone structure of Notre-Dame, where he finds refuge, further anchors him to the ground, unlike birds that soar freely in the sky.