The Bone saw is a medical tool owned by Evil Abed when he "crossed over" into the "Prime Timeline". It's a piece of surgical equipment which, as its name suggests, is able to cut through human bone. He got the device intending to use it to further his mission to darken the "Prime Timeline". Evil Abed was going to mutilate Jeff in order to make it more like his own "Darkest Timeline". Thankfully he was unsuccessful in his efforts due to a miscalculation and an unforseen change of heart. The bone saw's first appearance was in the Season Three episode "Introduction to Finality".
|In the study group's third year, Troy was forced to leave Abed and his friends to join the Greendale Air Conditioning Repair School. Abed retreats further into his own fantasies spending more time inside the Dreamatorium in order to cope with his loss. He imagines that "Evil Abed" had crossed over from "The Darkest Timeline" and taken over his body. His mission was to darken the "Prime timeline" and to that end he acquired a Bone saw. He planned to cut off Jeff's arm to remake him in the same image as his reality's Evil Jeff. He had a disastrous therapy session with Britta leaving her dejected before going to the Greendale Courthouse. Jeff was there arguing a case for Shirley over sole ownership of "Shirley's Sandwiches" with her business partner Pierce. On his way over, he donned a felt goatee as he fiddled with a bone saw he acquired.
|He arrived at the courthouse and plugged it in only to discover that the cord wasn't long enough to reach Jeff. Evil Abed then tried to motion Jeff to come over but he was too preoccupied with an ultimatum his old law partner Alan Conner had given him about the case. Frustrated, Evil Abed left to find an extension cord and returned with one a few minutes later. He plugged it in and was about to go cut off Jeff's arm when he heard Jeff's closing arguments which stopped him in his tracks. He was moved by Jeff's speech about selflessness, friendship and making the world a better place. This distraction allowed the "real" Abed to cast Evil Abed out and send him back to the "Darkest Timeline" ("Introduction to Finality").
|In the study group's fourth year at Greendale, Abed again uses his imagination to cope with reality after finding out Jeff will be graduating early this year. In therapy with Britta still, she gets him to retreat into a "Happy Place" inside his mind. This place takes the form of a television sitcom of his life called "Abed's Happy Community College Show". He imagines a typical musical sitcom introduction which features a montage of moments from the "sitcom". Most of these show the study group as they were in their first year (although Pierce has notably been replaced). In one of these moments, "Evil Abed" appears to be about to attack Troy with a bone saw. It's then revealed that Abed is fooling around ("History 101").