Freckles and Misery

I visited my parents yesterday, largely to celebrate my mother's birthday. While there my mother challenged me to explain why, for the past three summers, the postcards I have sent them have always featured a donkey. "Are you trying to say that we are like donkeys?" I don't know what I find more odd: that I have unintentionally favoured donkeys as symbols of relaxation and fun, or that my mother worries that her daughter thinks she is like a donkey (she is not, for the record).