Thanks I will definatly try that, and yes he is the youngest child.
it could really be either one. youll definitely want to get him checked out, and pay attention to his interactions with other people, his moods, any identifiable triggers, etc. if he is not mimicking anything hes seen, it could be jealousy. but its questionable.. try to maintain positive group interactions, make everything as equal, loving, and positive as possible, maybe cut out tv for a while and do something special with him, read him a bedtime story every night, have coloring time, etc. (coloring can be very good because children often depict their feelings in what they draw or draw memories, it could give you a clue), but definitely seek out professional advice because you want to combat this behavior now.
ADHD maybe but he could be jealous of the dog and his sister and mad at you because he feels neglected is he the oldest or youngest?