Explore the intricacies of JRuby implementation in this 49-minute conference talk by Charles Nutter. Delve into challenging aspects such as parsing Ruby, JRuby's parser, interpreter design, and native execution. Learn about JVM tricks, compatibility issues, and the complexities of string handling in JRuby. Discover the rationale behind crucial decisions, including fiber implementation and native integration. Examine Ruby's roots, the concept of layered runtime, and process control in JRuby. Gain insights into backtrace generation, command-line interface challenges, and strategies for improving startup time. Uncover the hard parts of JRuby development and implementation in this comprehensive presentation.