The solving instructions say "One square must contain a beetle showing possible alternatives to one of the [answers]".
I am wondering what the word "beetle" refers to here - from the context it looks like it could be two letters in one space, resulting in two equally-valid answers. From the overall thread of the puzzle, there could well be a few words differing by just one letter.
Also, of course, of you have two letters in one square - especailly if the one is written on top of the other - it would look like a squashed beetle.
I have trawled various X-word sites, but cannot find this as a technical term. any offers ?