This is just cruel.
Putting fun puzzles and quizzes on bar coasters is pretty common, but there should probably be a level of difficulty in which they do not cross. Basically, if a 4-year-old can solve it, it's probably safe.
[seealso slug="find-the-panda-puzzle-dudolf"]
For some Redditors, this puzzle was a little too intense -- or maybe they just had a few too many beers. In any case, here's the solution in case you need a little bit of assistance.