A first-year law student sent me a nice note the other day thanking me for turning her on to the beauty of the common law as an enervating force shadowing our social and political lives. She'd seen that Derek Chauvin, the cop accused in the George Floyd killing, had filed a motion to dismiss the criminal case against him. Chauvin claimed that had been trained to use exactly the type of restraint that led to Floyd's death, and his motion included pictures of training officers demonstrating it and excerpts from police manuals sanctioning it. While the outcome was tragic, Chauvin claimed he couldn't be found to have the mens rea needed to commit a crime when he was following to the letter the procedure he had been trained and ordered to employ in that situation. Reading the motion, she understood exactly what issues that were likely to drive the outcome of the case.