The front panel has connections for earphones, a ground, and an antenna (aerial).
The cat’s whisker detector is of special note due to the nicely ground crystal it rests upon. The ground crystal presents a smooth surface over which the whisker can easily slide. This increases the likelihood that a good conduction point will be quickly found.
References & Additional Resources:
A Homebrew Galena Crystal Radio Set Homebrew 1920s Crystal Set (ohio.edu)
https://people.ohio.edu/postr/bapix/CrystlRd.htm
YouTube video, Crystal Radio Sets of the 1920s and 1930s,