Komainu

Komainu , often called lion-dogs in English, are statue pairs of lion-like creatures either guarding the entrance or the inner shrine of many Japanese Shinto shrines or kept inside the inner shrine itself, where they are not visible to the public. 

The first type, born during the Edo period, is called sandō komainu , ]

the second and much older type jinnai komainu . 

They can sometimes be found also at Buddhist temples, nobility residences or even private homes. The komainu is also one of the pieces of a shōgi (Japanese chess) board.

Meant to ward off evil spirits, modern komainu statues are almost identical, 

but one has the mouth open, the other closed. 

This is a very common characteristic in religious statue pairs at both temples and shrines. 

This pattern is however Buddhist in origin (see the article about the Niō, human-form guardians of Buddhist temples) and has a symbolic meaning. The open mouth is pronouncing the first letter of the Sanskrit alphabet, which is pronounced "a", while the closed one is uttering the last letter, which is pronounced "um", to represent the beginning and the end of all things. Together they form the sound Aum, a syllable sacred in several religions like Hinduism, Buddhism, and Jainism.

There are however exceptions to the rule in which both komainu have

 their mouth either open or closed. 

The two forms are called collectively a-un and individually as a-gyō (阿形, lit. "a" shape?) and ''un-gyō (吽形, lit. "un" shape?).