Whereas earlier Japanese images showed Acala with glaring eyes and two fangs pointing upwards, a new variation developed by the late Heian period which depicted him with one eye wide open and/or looking upwards, with the other narrowed and/or looking downwards - an iconographic trait known as the "tenchigan" (天地眼), "heaven-and-earth eyes". Similarly, one of his fangs is now shown as pointing up, with the other pointing down. Acala's mismatched eyes and fangs were allegorically interpreted to signify both the duality and nonduality of his nature (and of all reality): the upward fang for instance was interpreted as symbolizing the process of elevation towards enlightenment, with the downward fang symbolizing the descent of enlightened beings into the world to teach sentient beings. The two fangs also symbolize the realms of buddhas and sentient beings, yin and yang, and male and female, with the nonduality of these two polar opposites being expressed by Acala's tightly closed lips.