This practice is a kind of contemplation on the illusory nature ("maya") of phenomena. Tilopa's oral instructions state: All animate and inanimate things of the three worlds are like the examples of an illusion, a dream and so forth. See this at all times, both in movement and in stillness. Contemplate an illusory deity reflected in a mirror; take a drawn image of Vajrasattva, and consider how the reflected image vividly appears. Just as that image is an illusory appearance, so it is with all things. The yogi thus contemplates the twelve similes and sees the reality of how all things are illusory. This is the instruction of mahasiddha Nagarjuna.