The worldwide collaborative effort for the creation of software is technically and socially demanding. The more engaged developers are, the more value they impart to the software they create. Engaged developers, such as Margaret Hamilton programming Apollo 11, can succeed in tackling the most difficult engineering tasks. In this paper, we dive deep into an original vector of engagement - humor - and study how it fuels developer engagement. First, we collect qualitative and quantitative data about the humorous elements present within three significant, real-world software projects: faker, which helps developers introduce humor within their tests; lolcommits, which captures a photograph after each contribution made by a developer; and volkswagen, an exercise in satire, which accidentally led to the invention of an impactful software tool. Second, through a developer survey, we receive unique insights from 125 developers, who share their real-life experiences with humor in software. Our analysis of the three case studies highlights the prevalence of humor in software, and unveils the worldwide community of developers who are enthusiastic about both software and humor. We also learn about the caveats of humor in software through the valuable insights shared by our survey respondents. We report clear evidence that, when practiced responsibly, humor increases developer engagement and supports them in addressing hard engineering and cognitive tasks. The most actionable highlight of our work is that software tests and documentation are the best locations in code to practice humor.