Who was THAT?

After putting her grandchildren to bed, a grandmother changed into old slacks and a droopy blouse and proceeded to wash her hair. As she heard the children getting more and more rambunctious, her patience grew thin.

Finally, she threw a towel around her head and stormed into their room, putting them back to bed with stern warnings.

As she left the room, she heard the three-year-old say with a trembling voice, “Who was THAT?”