xkcd #3125: Snake-in-the-Box Problem
Title text:
Chemistry grad students have been spotted trying to lure campus squirrels into laundry hampers in the hope that it sparks inspiration.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3125/
Took me a while to follow that too! The three examples of fails at the top each show instances where there are non-consecutive parts of the snake on adjacent corners - it's the lines highlighted in red.
Basically no two parts of the snake that aren't directly joined to each other in the snake are allowed to be on corners which are only a line apart.
I think.