'Supernatural': Dean stabs Amy Pond in the heart
So here’s the thing: when you’re dealing with supernatural beings of any kind, it is most important to always be prepared for anything and to take all precautions possible. For Dean, Amy Pond was a cautionary loose end Sam had left untied, and he went back in to finish the job. You could say he was ruthless about taking out the Kitsune who claimed to only kill in order to heal her son, but hey, in this line of work ruthlessness is actually something you want on a resume!
Source: (c) The CW