The extra key is a challenge key to expand the cut-way locks usefulness. Its has a more extreme biting (higher/low cuts) compared to the one which comes initially. The idea is to re-pin the lock to suit the challenge key and try to pick it again. You’ll find its far more difficult and be great practice for when facing similar extreme biting on other locks.

Mix the challenge key with some security pins and you have a far more useful product to provide many hours of learning.