This is really hard to describe so bear with me.
My daughter has just started to do this. She does it mostly in her high chair or her car seat. She holds on to the arms of the high chair with straight arms and holding on tight. She in really concentrating (for example if I am tryin to feed her she doesn't even notice I have a spoon in my hand). Her legs are clenching and it looks like her bottom is clenching. I have come to the conclusion that it is a habit or her bottom is itchy. She is 10 months old. She doesn't seem in any disctress.
Has anyone else had this??