A severed head killed a man.

Sigurd Eysteinsson was a leader in the Viking Conquest of what is now northern Scotland. Near the end of his reign, Sigurd challenged a native ruler named Máel Brigte the Bucktoothed to a 40-man-a-side battle to “settle their differences.” 

Brigte agreed, but Sigurd deceived him, and brought 80 men. Brigte immediately knew he was defeated and told his men “kill at least one man before we die ourselves.” Sigurd's army quickly defeated Brigte's, and as trophies, Sigurd's men strapped the severed heads of their enemies to the saddles on their horses. 

On the return home, Brigte's head, which was hanging from Sigurd's saddle, scratched Sigurd's leg with his bucktooth. The leg became inflamed and infected, and Sigurd died as a result. Quite a strange testament to the existence of karma, don’t you think?