I noticed that turtle can't fit through the diagonal spaces between
blocks. Must be the hard shell!
Actually, that was intentional. The first time I encountered an astar
pathfinding routine written in Pygame, it let them 'cheat' by going
between diagonally lined up blocks. You can disallow it by having your
routine check diagonal blocks in addition to blocks to the left and
right. It has a side effect of allowing the path to go in a diagonal
direction too.
Feeling a blog coming on...
I'll have to go check it out! I like your blog. :-)