No usage of saliva
Saliva ban was a big debatable topic before the ICC confirmed the temporary banning of the natural substance. Saliva is used to shine the ball which helps the fast bowler to swing the bowl while spinner gets help to drift the bowl.
However, now saliva has become the transmitter of the deadly COVID-19 so it was necessary to ban its usage. So, it will be interesting to see in the Test series how the bowlers will tackle the situation without any aid.