There are 3 squares with 5 crossed lines on their edges. If you go into a square you must come out, therefore meaning you need an even number of crossed lines to get in out, in out of a square. If the number is odd, you must end or start in that square, but as there are 3 odd squares, theres one left.
But, as always with these things, thats what im MEANT to think, there will be a solution.
Top right box - haven't crossed the line -- or if you have - you've come back over the line
2 second attempt
2 second attempt
? Me, not, follow. :s
2 second attempt
This
Nope..