Serious. Ask IJUSTWANNASURF, there are generally 2 ways of doing the footlock. A lot of people pinch the Achilles with their forearm to get the tap. It can for sure damage the tendon and cause damage, but most people usually tap to pain, and if they have a high pain tolerance, it can be harder to get a tap.
The other wway is the kinds people like Braulio, Aoki, Hall, Garcia, and others use. They try to get the top of the foot under their armpit and against their ribs, and they use their body to bend the top of the foot down, basically trying to pry/tear the foot off and away from the ankle.