The kama is a traditional farming sickle, and considered one of the hardest to learn due to the inherent danger in practicing with such a weapon. The point at which the blade and handle join in the “weapon” model normally has a nook with which a bo can be trapped, although this joint proved to be a weak point in the design, and modern day examples tend to have a shorter handle with a blade that begins following the line of the handle and then bends, though to a lesser degree; this form of the kama is known as the natagama.
The edge of a traditional rice sickle, such as one would purchase from a Japanese hardware store, continues to the handle without a notch, as this is unneeded for its intended use.
[From Wikipedia. More here]