Bizarre story, that I can’t say I fully understand.
But here’s the thing: You don’t want to believe your grandmother is poisoning you. You know that she loves you—there’s no doubt of that—and she’s so marvelously grandmotherly and charming. And you know that she would never want to poison you. So despite your better judgment, you eat the food until you’ve passed out so many times that you can’t keep doubting yourself. Eventually, we would arrive for holidays at Grandma’s with groceries and takeout, and she’d seem relieved that we wouldn’t let her touch our plates. By then, her eyesight was starting to go, so she wouldn’t notice the layer of crystalline powder atop that fancy lox she was giving you.