depends. is it a murder of passion? or convenience?
because if it was planned and the murder already had the object, then i would definately go with the carving knife. a knife just seems more personal. also, there would be multiple knife wounds, not just one. the murderer would stab even after the death,
but say, for example, these two people were in a room, and one just gave the other horrible news, that could ruin him forever. the latter would simply grab the closest object to kill with. scissors are usually left out, possibly on someone's work desk. when the man turns his back, the second, without thinking, grabs the scissors and plunges them into his back, but only once, until he notices what he's done. he hides the body, then flees.
but, this is how i would write it
hope this helps?