LOL that is priciously the hardest part to describe... lemme... try find some screenshots...
EDIT: I should say.. if there's 2 turns involved, one of them must be "immediate"....
Double EDIT:
Like in the red line, you'll need to go straight up two tiles, around two turns to get to the other tile... that wont let you pair up the tiles
Where as in the yellow one, straight after the left tile the path turned.. then it can turn again at anytime to reach for the next tile...
Does that make better sense?