Milk and Poison by Ellen B. Luborsky
[…]What had I done? I thought my words would be harmless, a mere repetition of hers with a millimeter of meaning attached. I had hoped they would let her know I heard her. How did I alarm her instead? She had been pouring poison in and out of her cup until my words stopped her, as if the poison turned real when I spoke. I should never have linked play with harm. It was weeks before she would come near me again.