If this lesson has one takeaway, it’s that memes aren’t facts. On this week’s Last Week Tonight, John Oliver examined how the strange persistence of fears about the dangers of vaccines has led to all sorts of dangerous public-health issues, including a recent outbreak of measles in Minnesota. You may have heard a few of these arguments before, but it’s worth it to hear John Oliver using sex with donkeys as a way to explain how you can’t prove a negative, and for his truly stellar use of fake inspirational quotes.