Being able to laugh silently is a very useful skill, and I learned this skill with I was about 11. It's not how I prefer to laugh, but it's something I can muster in the necessary circumstances. It's admittedly, not a completely silent laugh, but quietly enough that only someone fairly close by could hear the quick breaths and small convulsions of laughter. The situation in which I honed this skill was in sixth grade during a fairly pointless homeroom class. The idea of homeroom is that it's sort of an administrative class: you gather a cohort of students, take attendance, tell students about any new changes and perhaps give them a chance to study or do homework for other classes. In other words, no teaching usually goes on. Homeroom at this time was particularly boring. It did help, though, that I'd made a friend in my homeroom, also named Joe. To distinguish each other he decided to call himself "Joe One" and me "One Joe," but those nicknames never really stuck. Joe and I would sit in the back of the class and trade jokes, clever quips and whatever else is prone to make an 11 year old male laugh. And we laughed a lot. Hence the need to learn to laugh silently, so that while our homeroom teacher prattled on about, whatever, we could laugh and enjoy ourselves.