I record this quotation for Google, because I'm happy to finally run across it again. (It's something Anscombe told Bryan Magee in conversation, apparently. This is why I never could find it in "Culture & Value" when I looked for it there. The context is Magee's wondering why Wittgenstein doesn't mention Schopenhauer more.)
From Brian Magee's "The Philosophy of Schopenhauer":
[Wittgenstein] used to say that if a man had been physically nourished on bacon and potatoes we should all see the folly of trying to identify which bits of his person derived from bacon and which bits from potatoes, and yet we make exactly that mistake with regard to whatever intellectual nourishment he may have metabolized into himself.