When Ranma was ten/six years old (manga vs. anime), Genma tried to teach him the Cat Fist. He tied fish sausages around Ranma and tossed him into a pit of hungry cats, presumably with the belief that this would imprint the fighting movements and instincts of cats into Ranma's mind. However Genma had made the critical mistake of not fully reading through the description of the technique, which stated that nobody should try and train a person in the Nekoken through these methods. He tried to cure Ranma by repeating the process with dried sardines, salted sardines, and fish cakes, but these attempts had the opposite effect and only exacerbated Ranma's fear even more. Despite this, neither have sought or attempted to cure Ranma's phobia since, and it is never mentioned how to actually train someone in the technique. Assuming that there is a "proper" method and this is not merely one of the oddities of martial arts histories; whilst the manga has the "next page" stating that only an idiot would try to teach someone the Nekoken, the anime has it declare that the move has been banned for the severe psychological distress it forces on the trainee.
When Ranma falls into his cat-like state, he starts acting like a cat, apparently using his power more efficiently by fighting like a ferocious animal, with swipes of his "paws" which have torn tree-trunks to shreds from a few meters distance. This does not seem to be the result of chi-blades, since no visual effect has implied it while they were clearly distinguishable when generated by Herb. Rather, Ranma's "claws" seem to be powerful air pressure swipes, somewhat similar to those of Tatewaki Kuno or Ryu Kumon, but with far less shown destructive power than the latter. While in this condition, he even managed to disperse Cologne's Shark-Fist water blast, though it is uncertain how much she held back, or to tear effortlessly through the ice boulders wielded by her Fist of the Ice Bear technique.
However, the mental influence of this technique goes beyond merely giving Ranma enhanced fighting instincts. Ranma's "cat mode" is so powerful that, mentally, Ranma truly becomes a cat, driven by instinct and suffering severe impairment to both intellect and attention span. This is the great weakness of the technique, making Ranma vulnerable to both catnip (which will make him "drunk") and distraction (throwing something and saying "Fetch!" has proved enough to get rid of him), as well as being completely incapable of strategizing or using any level of higher thought. This makes the technique virtually useless, as Ranma in cat-mode is completely unpredictable; there is no way of controlling who he attacks or how badly, and he is just as likely to get bored or scared and run away from a fight as he is to stand his ground.
Ranma cannot remember what he does when in his cat-like state. He has been brought out of the Nekoken by being doused with water, or by falling asleep in the lap of someone he trusts. This used to be an old woman who lived in the Saotomes' neighborhood, but is currently Akane Tendo.
Also worth noting is that Ranma and Akane shared their first "kiss", while he was in this state, as he impulsively rubbed his face against hers, and it was believed to be a kiss by everyone watching. Although Ranma did not recall doing this, Hikaru Gosunkugi later showed him photographic evidence. This was not Ranma's first kiss however, which he received from Mikado Sanzenin while in his female form, to his tremendous embarrassment.