A traditional Thursday afternoon qat-chewing and tobacco-smoking session among friends in Sanaa, Yemen, can last five or six hours. (From the book What I Eat: Around the World in 80 Diets.) The men pick through the bag selecting leaves to chew until the masticated mass in their cheek is the size of a golf ball. Qat is harvested year-round. Its leaves lose their potency within a day, so they must be picked, sorted, washed, and rushed to market daily.