Ruby-core is where Ruby features are born and bugs gets squashed. Get a glimpse of what this entails and test your Ruby knowledge and intuition at the same time. How surely can you differentiate unexpected behavior from normality? How in tune is Matz's principle of least surprise with yours? Can you distinguish bugs from features? We will figure it out through a series of questions inspired by actual bug reports and feature requests, spiced up with a couple of trick questions. Each question is a dilemma and everyone gets to pick if they think it's a bug or a feature. To uncover the answers, we'll have to explore unchartered territories. We'll dig deep in recursion, battle failing specs, encounter exotic Floats and other infinities, and decipher arcane C code. Rubyists of all levels, from beginners to hardcore pros are invited in this informal challenge. Be sure to check your ego at the door, as no-one will escape unscathed; even top notch ruby-core committers don't always get right answers! Let's discover what can lie under the apparent simplicity of Ruby without forgetting to have fun.