Venus in sidereal Cancer and the lunar sign, Ashlesha is associated with serpents and poisons. Interestingly, I had a conversation at an art gallery (Venus) a couple of days ago about drug use and spiritual experiences.
Ashlesha is associated with Patanjali of the Yoga Sutras. This shows the knowledge required to overcome the slippery pitfalls of spiritual practice; the attachment to the siddhis (magical powers) is just one. Once our attachments (Cancer) are overcome, yoga is possible.