The act of inserting ones arm into anothers vagina. Unlike fisting the hand is kept open. The person initiating the bonesaw then thrusts their arm back in forth in a sawing motion. While this is all going on the bonesawer is screaming "BONEEEESAWWWW" as loud as they can. This usually results into the one receiving the bonesaw walking very awkward and in a post-sexual manner. Those who are doing the act of bonesaw or being bonesawed are usually called out in school hallways, assemblies, or public places from those yelling "BONEEESAWWW" very loudly and obnoxiously while bonesawing their own arm up in the arm for all to see.
Guy 1-"I bonesawed the shit out of Peggy last night. I think I tore her to shreds with my arm."
Guy 2-"I'm gonna tell everyone to throw up bonesaw at her and you at school tomorrow"