4 year old obsessed with bones

My son is 4 and will be 5 in January. He is going through evaluations for development because he is a little odd and his big sister is autistic. But we are just at the beginning of it. He scored clinically significant in hyperactivity. Depression, and anxiety with the school district and I am on the hunt for a child psychologist for testing.Ok, so to the point. At 2 yrs old he was asking to watch anatomy videos on you tube. I was very selective of the videos and stayed with what looked appropriate for a two year old. Then we went through a phase where he wanted to see real organs. Even asked me to see mine because "All I would need is a knife." So we talked about pain, and hurt etc... knife into people = hospital. He understood and never asked that again lol. He is pretty literal so based on his personality it really wasn't a scary thing.So we got him a human body figure with removable organs and he learned all of the organ names and what they did. We got him a kids heart model and he wants a brain model this year.So at three he wanted to be a surgeon but lately he said he wanted to be "an investigation of dead people when they are bones"He doesn't play with very many toys except his microscope, play dough, we make slime, roblox, and plants vs zombies. We play out side a lot, we go fishing, and camping/exploring often.I'm trying to think of other ways to get him engaged. He does like doing simple addition and we have workbooks that he likes to do that or science-based. He is a little bit behind in the age appropriate sections of academics. So we are working on those. But we have to make it interesting. Rewards do not work often. And often back fire for some reason. Last time we did a sticker chart he ripped it off the wall.Some one else has to have a smarty pants like this with some strategy. He is not very cooperative either at home. At school he is more easily redirected so we have been doing more positive reinforcement at home like his teacher does. We are close with his teacher too so that helps. I watch her son while she teaches mine.He likes to feel people's hair and eye brows too. Lol. Very sensory based little boy.Super verbal and communicates way above average. So his pediatricians do not think it's autism like his sister. Who is also super verbal but more academically challenged. via /r/Parenting http://ift.tt/2yMWaA0