Here is a link to a video of an accident that occurred at Shop At Home Network. This could happen to any sword that is not safe to use, including:

Japanese sword imitation,
Japanese inferior junk sword made in China,
Japanese sword that was not properly and correctly heated and hardened,



This list does not exclude some of the authentic Japanese swords with the following condition(s):

Authentic Japanese blade that has hamon (hardened temper edge) completely or partially missing,
Authentic Japanese blade with chip(s) or crack(s) cutting through the width of the hamon (hardened temper edge) complete,
Authentic Japanese blade tang attached to a loose or weakened handle,
Authentic Japanese long katana length blade, with a short wakizashi length tang attached to a much longer handle.
Authentic Japanese blade that was retreated with high heat, or with the blade and the tang re-welded together.

http://www.youtube.com/watch?v=7e77oXjFkIs