Horus Pet House

Horus Pet Shop is a pet shop located in School District 7 within the confines of the School Garden. Kongou Mitsuko of Tokiwadai Middle School uses it to appropriate food for her snake, Ekaterina.

Etymology
The pet shop is named after an ancient Egyptian deity of the same name. Furthermore, seeing as Pet Shop the bird of Jojo Bizarre's Adventure fame is used in the logo in the original manga, may be a reference to the bird's Stand, called Horus. Moreover, it may be a reference to the Aeon of Horus.

Toaru Kagaku no Railgun
In the original manga, the pet shop is introduced during Misaka Mikoto's showing of Mitsuko around the School Garden. After Mitsuko asks about wanting to see a pet shop, Mikoto takes her to the Horus Pet Shop.

The scene is later adapted in the Toaru Kagaku no Railgun S anime, where Mitsuko later urges Shirai Kuroko to accompany her to the pet shop as she buys food for Ekaterina. Here, Kuroko bumps into a tortoise, where she gets an idea to use turtle meat for a nabe with her friends later that evening.

Trivia

 * It's logo in the original manga is a reference to two animals from the Jojo Bizarre's Adventure franchise, Iggy the dog and Pet Shop the bird. The reference however is lost in the anime adaptation.