If the thumb grips too much
The teacher should try taking the child’s bow away by surprise, to see if it comes away easily or not.

The teacher should try taking the child’s bow away by surprise, to see if it comes away easily or not.
Stretching the arm is a way of telling the child to make sure that his thumb muscle is relaxed.
This can be practised by taking the thumb right away and putting the little finger under the button.
Crooked bowing may depend on: