Family is coming to visit!

Why is it that I start freaking out about the cleanliness of my house when my parents are coming to visit? I think there is something ingrained in us as children (probably only female children) that kicks in, as if our mothers are going to walk in with a white glove and do a spot check to see if our house is "clean enough." Of course, my parents have reassured me that they don't care how clean or dirty my house is. But if you happen to try and call me on Thursday night, I might not be able to hear you over the vacuum cleaner.