1.   This requires a level of co-ordination in tongue movements and swallowing.

2.   Our larger canal presumably reflects a bigger hypoglossal nerve, giving us the precise control over tongue movements that we need for speech.

3.   In addition, when we are sleeping our self-cleansing mechanism - the saliva production and the tongue movement - is reduced.

4.   Older drugs carry the risk of movement problems like rigidity, tremors, grimacing, lip-smacking and tongue movements.