Yes, a genuine Katana can sever a person's throat in one blow. The sharpness and flexibility of this blade are legendary. Yes, you can cut someone in half (ideally one with a tiny waist), especially if you're riding a horse and have enough speed. However, it is very difficult to do so effectively.
The truth is that cutting someone in half is not easy. They need to be very thin and well balanced to avoid being splintered in many pieces. Also, the force needed to execute such a strike is huge. You probably won't be able to do it with just one stroke; rather, it will likely require several strong cuts.
In conclusion, yes, a katana can cut a man in half. But only under the right circumstances. It takes great skill to use these knives without killing your victim.
Can a katana truly chop a person in two as in the movies? Yes. If you think about it, it doesn't take much strength to accidentally slash oneself rather deeply, therefore an intended cut can surely cut through skin, muscle, and bone, especially in the hands of a competent swordsman. In fact, several historical swords have been found with cuts deep enough to go through the hand and arm.
However, this does not mean that they always did. For one thing, there is no evidence that any samurai ever deliberately sliced themselves in order to gain honor or immortality. They might do so in the heat of battle, but this is not the same as acting out of malice.
Furthermore, even if they did, their wounds would have been treated immediately, because stopping blood flow from an injured limb was important in order to prevent amputation. A severed artery could also lead to death, so caution and skill were needed when using a sword.
Finally, consider that most samurai swords were made of steel. While they can certainly cut through flesh and muscle, they are not meant to be used as butcher knives. If you look at actual battle scars from swords that were actually used during wars, you will see that they are usually only about 1/4" thick. The rest of the body is covered in many more layers of skin which protect us from the sharpness of the blade.
True, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true A katana, not an axe, is a slicing weapon. It has the ability to and does cut quite deeply and effortlessly. It has the ability to remove limbs, although cutting all the way through a torso would be difficult and futile. Your sword would most certainly become entangled. It has the ability to penetrate armor, but only at close range. A sword can be used as a stabbing instrument at short range, but it is ineffective at longer distances.
Thus, a katana can kill you. However, it would take multiple cuts from several different people to accomplish this task.