He also will hide his poopy underwear behind his dresser, behind the bathroom door or under the bed....
Of COURSE the doctor has a very valid point, but do not automatically assume the worst. My brother is seven years younger than me. He started visciously rubbing his hands together and making a revving noise back when he was two years old. It looks like all his muscles get tense and he is seriously focusing. He holds his hands like as if you were holding your spouses hand (fingers not interlocked) and rubs them together. He would never tell anyone why he did this, but I am very close to him. When he turned 7, he told me that he does it when he imagines things, for example a train running off the track, or a tractor pulling a trailer. He said he just thinks really hard and pictures those types of "boy" things. He is now 14 years old and STILL does this, less often of course, but still very frequently... even daily. Some children have strange habits.My only concern would be the twitching, but don't freak out and good luck!!!
This sort of behavior can be typical of some children who display certain types of developmental disorders, and it will also be important to rule out any seizure activity. The first place to turn is to your child's pediatrician, who can refer the child to a pediatric neurologist.