I have a full grid and confusion over the thematic items. To get from the end of clue 3 (at 5, 2 in x-y notation) to the start of clue 4 (at 2, 4), I need a ladder: okay, so far, so thematic. Similarly to get from the end of 19 (9, 11) to the start of 20 (8, 4), I need a snake, but I can see no path between those two cells that spells out an appropriate word. More worryingly, I only seem to need seven thematic items to get from start to finish.