Witcher Potions: Cat
Cat: The Cat potion is one of the milder potions a witcher can take. Cat widens the pupils to the farthest possible dilation to grant witchers sight in total darkness.
- Cat (1 hr): Grants sight in total darkness.
- Enhanced Cat (2 hrs): Also provides some protection against hypnosis.
- Superior Cat (3 hrs): Grants complete immunity to hypnosis while allowing sight in complete darkness.
The main side effect witchers experience on Cat is headaches due to venturing out in sunlight when their pupils are still dilated and cannot be contracted enough to narrow in bright light. Witcher can naturally expand their pupils at will, but this potion takes it further and makes various muscles in the iris engage or relax: Iris sphincter relaxes (the circular muscle in the iris that constricts the pupil), the iris dilator muscle contracts (the muscles running like spokes from a wheel; they dilate the pupil).
Being out in sunlight brighter than early morning will be very painful to witchers, leaving them seeking out dark places to rest until they can control their pupil size again.
As for how Cat results in making witchers immune to hypnosis, no one knows. It seems to be a handy side effect that cannot be explained.