What unique characteristic connects these six words?
Update: SOLVED by Rich B. in the comments (nice work!), so there are spoilers below. I’ll keep the solution down there for now so you can noodle on the puzzle.
Yes, this is hard. (At least, it should be. Someone’s going to solve this in 30 minutes and prove me wrong now.)
Make your guesses in the comments. I’ll let you know if you’re right or wrong.
As time goes by, if this remains unsolved, I’ll add clues by editing the post. I may or may not decide what clues to give based on comments or questions, so feel free to noodle.
I won’t reveal the answer before someone solves it.
Any questions? Any guesses?