Today my almost 2 year old DS was playing with blocks at playgroup when he suddenly stood still, clenched his jaw so tightly that it quivered slightly with the effort, and he had his hands in fists. The whole time he stared in my eyes, and it probably only lasted about 2 or 3 seconds. Immediately afterwards he looked at me uncertainly, as he could tell by my face I was worried. I sat down in front of him and said (no doubt stupidly) "No, we don't do that, do we?" and he got a bit annoyed, and tried to move me away.
He did used to do this more often (maybe once every week or so), but hasn't for months. I always put it down to being a tic, something he does when excited, but now I'm not so certain.
Any thoughts? Thanks in advance.