My 2 year old DS has a funny habit that i have only just noticed in the past couple of days...

I will try and explain the best i can...

DS and I were putting blocks back into the shape sorter and i noticed everytime i would give him a block he would look at the shape sorter then he would say "ummmmm" and shake his head at the same time.
He did this everytime i gave him a new block.

He seems to do it when i ask him a question and its always the same thing "ummmmm" and shakes head at the same time....

Is that normal? or just one of those funny little things that kids do??