This week's very geeky NERD ALERT Xmas Special is brought to you by the number 78. Now, we all know Santa is real, but what kind of scientific time and motion physics caper is at play here that allows him to achieve his appointed workload and deliveries? Cue segue ... Xmas is a time for friends, family, eating, and laughter, so in this holiday season special, Dr Karl and Adam take a look at nut allergies and the physiology of laughter.