Knife Through Arm by Murphy's MagicKnife Through Arm: A Professional Illusion Built to Be Believed.. The Effect In full view, you press a solid steel knife directly through your own forearm! No covers! No hesitation! The blade visibly penetrates flesh, stopping your audience cold as disbelief turns into stunned silence. At any moment, when tension is at its peak, you have the option of releasing blood on command, transforming shock into absolute conviction. Then, just as cleanly as it