Agatha Christie is the queen of the Whodunit. Of the nearly 80 murder mysteries she wrote, about half of them involve death by poisoning.

Christie had an extensive knowledge of drugs and poisons because of her time spent working in a hospital pharmacy during World War I. She watched carefully as pharmacists and nurses administered medicine to patients, and she learned what dosages were safe, along with what could kill someone.

Luckily for the world, Agatha used her knowledge for good and wrote some of the most successful novels of all time. In fact, she’s only been outsold by the Bible and Shakespeares’ works.

On National Authors Day, celebrate from favorite storytellers by cracking open a good page-turner.

Today we also celebrate: Autistics Speaking Day, National Cinnamon Day, National Brush Day, National Family Literacy Day, National Cook For Your Pets Day, National Calzone Day, National Biologic Coordinators Day, National Vinegar Day, and National Deep Fried Clams Day.