Here steps are shown in preparing a toy which encourages the child to pull off the string
... and maybe to wind it up again.
A Mini Ladyshaver. The blades have been removed and some square and triangle buttons are tied to the top of the shaver. When the child moves this to his mouth, the vibrations through the buttons give a funny sensation on the lips and teeth. This may encourage him to mouth-centred manipulation of shaver and buttons resulting in further mouth motor development.
Other materials can be added to the shaver - maybe encouraging the child to be curious and experimental.