in chapter four what is strange about the cat's behavior

The cat was taking advantage of Zeena's absence and lounging around unnoticed.

"The cat, unnoticed, had crept up on muffled paws from Zeena's seat to the table, and was stealthily elongating its body in the direction of the milk-jug, which stood between Ethan and Mattie. The two leaned forward at the same moment and their hands met on the handle of the jug. Mattie's hand was underneath, and Ethan kept his clasped on it a moment longer than was necessary. The cat, profiting by this unusual demonstration, tried to effect an unnoticed retreat, and in doing so backed into the pickle-dish, which fell to the floor with a crash."