Need to vent a bit. Nothing against the challenge itself, but against my own stupidity. Spend an hour banging my head against the challenge, managing to pass various parts of it even. But for the life of me I could not get it to work. In the end, and with a tremendous amount of shame, I gave in and looked into the hints for the spoiler.
And I realised that it did not occur to me to store the .shift() as a new variable and return that. God now I feel like digging myself a big deep hole.
Anyway the morale of this story is, if you think you tried everything, take a deep breath a see if there is something (no matter how crazy) that you can do.
All the best coding!