Such a bloodied claymore has history way back through lines of father and son. In fact only one place near the handle still holds a metal tone, because of a magical barrier, and it has ingraved in it words that forever speak out to the swords bearer. Those words, like a guilty memory, can never be forgot.
“Thou who shall kill a sons father, shall then be killed by a fathers son.”
If a creature is transformed into another creature (say, a human into a dog), then that creature will become more and more accustomed to the new form until a point is reached where reversing the spell is impossible. A second transformation is possible, but the creature will have to go through the whole process again.