Final answer:
In the book Because of Mr. Terupt, Mrs. Williams covers her mouth with her hand when there is a surprise coming.
Step-by-step explanation:
In the book Because of Mr. Terupt, Mrs. Williams does something when there is a surprise coming. In the book, Mrs. Williams is known to cover her mouth with her hand when she is surprised. This is mentioned several times throughout the story as an indicator of her surprise or shock.