Tension, attention or relaxation: A cat's whiskers tell us a lot about our pussy cat's mood. It is not clear why the horny vibrissae around the mouth, above the eyes and on the back of the front paws were given the name 'hairs for purring' in German. The extremely touch sensitive antennae have nothing to do with purring.

'First of all whiskers are sensory organs,' says cat expert and author Dr. Helga Hofmann, 'they are like sensors for the close-up range.' They protect a cat from eye injuries, enable her to inspect things that are very close but outside her range of vision, and help her to move around safely in the dark. However, there's even more.
'The long whiskers on the upper lip indicate the cat's mood,' says Dr. Hofmann.

Here's a short guide to reading those 'whiskers':
• whiskers stretched to the sides and slightly hanging: quiet, balanced mood, the cat is ready for a nap.
• whiskers slightly tilted to the front: attention.
• whiskers spread out to the front: growing attention, the more spreading the more tension, readiness for action, in combination with 'playing' ears this can mean annoyance and aggressiveness.
• whiskers laid back: limited curiosity, caution, aloofness, however no discomfort if the ears are upright and the tail is relaxed.

'In order to understand the body signals of our pussy cat correctly, it is important to see them in relation to each other,' the cat expert advises. 'An example: laid-back ears can indicate fear as well as aggressiveness. When you look at the whiskers, the situation becomes clear: if they are spread out to the front, you can assume that your cat will soon attack her counterpart. If the whiskers are laid back close to the face, fear is the predominant mood.'

Source: IVH