At a cryptocurrency conference in Switzerland, a former Royal Marine taught Bitcoin investors how to break out of plastic restraints by biting through them. The gathering in Lake Lugano, near the Italian border, aimed to address rising concerns among wealthy crypto investors about being targeted in kidnappings and ‘wrench, attacks’, where attackers may resort to physical force to obtain passwords. Pete Kayll, a musclebound veteran of Britain’s Royal Marines, had an unusual instruction for the Bitcoin investors gathered in Switzerland in late October. ‘Just bite your way out,’ he told them. It was the final day of a weekend-long cryptocurrency convention. A small group of investors had lined up in a conference room to have their hands bound with plastic zipties. Now they were learning how to get them off. ‘Your teeth will get through anything,’ Mr. Kayll advised. ‘But it will bloody well hurt.’