As with any good hypnotic curse this one starts small, increasing any existing interest in anal or awakening one that never existed.  As time goes by the desire grows, a mild interest turns into an interest in porn that has anal in it that leads to experimenting with anal which results in you wanting anal.  Left uncontrolled the listener will eventually only get pleasure from sex that has some anal element and from filling their ass with various plugs and toys.  Only EMG can remove this curse.