The right hand side, when reflected back upon itself, reveals a bull-like, horned demon, flanked by two guardians.
The left hand side reveals a powerful, apocalyptic scene of crucifixion.
The use of magical mirrors is a well known feature of sorcery. Magicians can use mirrors to compel personal demons to appear. Once accomplished, the magician can free himself from the demon's power.
Freeing himself from demonic influences is a form of self-exorcism which appears to have been one of Picasso's motive in concealing such images in the drawing. This is relevant , in the context of Picasso's overpowering psychological feelings of crucifixion and melancholy he was experiencing in 1934. The images are also relevant to Picasso's vision of the inevitable apocalypse which was soon to be unleashed by Hitler.
The images above are shown in negative.