The male Nidoran has developed muscles that freely move its ears in any direction. Even the slightest sound does not escape this Pokémon's notice.
(From Bulbapedia)Nidoran♂ is a small, quadruped rodent-like Pokémon. It is pinkish purple with darker spots, and has large, spiny ears with teal insides, oversized front teeth, and red eyes. Its back is covered with three lines of large spines that can release potent poisons if threatened. The center line of spines is taller than the other two. The size of the long, pointed horn on its forehead is indicative of the strength of its venom. Nidoran♂ is an exclusively male Pokémon, Nidoran♀ being its female counterpart.
Nidoran♂ constantly listens for the sounds of approaching enemies with its large ears. Said ears have unique muscles that allow them to be moved in any direction, and even the slightest sound does not escape Nidoran♂'s notice. In order to listen to distant locations, it flaps its ears like wings. When angry, it extends its toxic spikes and charges, stabbing with its horn to inject poison. Nidoran♂ lives in open spaces, such as savannas and plains.
(From Bulbapedia) Nidoran♂ appears to draw inspiration from hamsters, rabbits, or – given their aggressive nature towards one another – porcupines, with aspects of venomous mammals. However, anatomically they are arguably most like hyraxes – small, rodent-like mammals that are genetically more closely related to much larger mammals like elephants and manatees featuring thickset bodies with tough hides (similar to Nidorino and Nidoking).
(From Bulbapedia)Nidoran♂ may be derived from needle. It may also come from cnidocyte, a type of venomous cell responsible for the stings delivered by stinging animals, most notably jellyfish. Alternatively, it may be based on 二 ni (two) or 二度 nido (two times/two degrees) referring to the two distinct evolutionary lines with similar names and traits. Also, the Japanese word ran is translated as orchid in English. Orchids are flowers that can be purple or blue, these being the same colors as the male and female evolutionary forms of Nidoran, respectively. The ♂ is an indication of its male gender.