I recently finished reading the book "State of War: The Violent Order of Fourteenth-Century Japan" by Thomas Donald Conlan. Below is an explanation of an interesting (and gruesome) samurai practice from the 1st chapter of the book.
The act of taking an enemies head in battle has a long history in Japan and was infused with a significant amount of cultural meaning and usually generated praise from authorities. The main purpose of taking a head was to prove one's battle service. Heads were rigorously inspected because they constituted the most tangible proof of battle service. The heads of those killed would be carefully cleaned and dressed, and names attached to those who could be identified, while those determined to be from low-ranking men would be discarded.
Generals sometimes discouraged the custom of head-hunting because warriors so engaged might become vulnerable and place themselves in grave danger. Those who were successful tended to abandon the battlefield, already in possession of the ultimate proof of valor. Some commanders issued standing orders to "cut and toss" these heads. In these circumstances, warriors discarded the heads once their valor had been witnessed.
Those thirsty for some token of achievement decapitated any wounded enemy they could find. For wounded men to spend a night unscathed on the battlefield was described nothing short of miraculous. Prior to the fourteenth century, warriors were praised for securing as many heads as possible. For example, during the Mongol invasion of 1281, a samurai named Kikuchi Jiro advanced among the Mongol dead (or almost dead), collected a large number of heads, and brought them into the castle, thereby making a name for himself for generations.
Although some warriors continued to matter-of-factly pick up discarded heads, a stigma eventually accrued to such scavenging. Rules of etiquette eventually were established regarding the taking of heads. Transgressors of the norms of head-hunting became the objects of laughter in the 1330s and the focus of scorn in the 1390s. The practice of picking up an abandoned head gradually became a shameful act, and so later military manuals devoted considerable detail to distinguishing whether a head was removed from a living man or a corpse.
The book also described how warriors during this time period joined the forces of one side or another based mainly on the anticipation of great reward, generally in the form of land. This as well as the practice of head hunting go to show that the samurai warrior was not always the honorable warrior devoted to and willing to die for their lord. This image of the samurai comes from later time periods. And even then it is still largely a myth. The samurai throughout history are well known to engage in treachery and deceit. They often changed sides in the heat of battle or turned on their lords.