The Reptile House is a building at the zoo which the Dursley family visited for Dudley Dursley's eleventh birthday in the summer of 1991. The interior is described as cool and dark, with the only light coming from the large, glass-fronted displays that line the walls. These enclosures house a variety of lizards and snakes. The most prominent enclosure held a large Boa Constrictor, which was noted on its sign to have been bred in captivity. It was described as being long enough to crush the car the Dursleys drove and was a “dull, muddy brown” color. This is the only known history of the location, as its sole appearance is during this single event.
The Reptile House is the site of the first significant, public display of Harry Potter's uncontrolled magic and his first known use of Parseltongue. During the visit, Dudley Dursley and his friend Piers Polkiss grew bored when the Boa Constrictor remained asleep. After they moved on, Harry Potter began speaking to the snake, apologizing for his cousin's behaviour. To his surprise, the snake responded by raising its head and winking. This was the first instance of Harry communicating with a snake, though he did not understand the significance of this ability at the time. When Dudley saw the snake was active, he shoved Harry violently to the floor to get a better look. In a flash of anger, Harry unknowingly caused the thick glass of the enclosure to vanish completely. The Boa Constrictor uncoiled itself and slithered out onto the floor, causing panic throughout the Reptile House. As it passed Harry, the snake seemed to say, “Brazil, here I come… Thanksss, amigo.” before heading for the exit. The incident resulted in Harry Potter being locked in his cupboard under the stairs for the longest punishment he had ever received, which directly preceded the arrival of his first Hogwarts acceptance letter. This event foreshadowed his connection to snakes and his status as a Parselmouth, a crucial element in Harry Potter and the Chamber of Secrets.