Luckily for you, it would seem Applejack was considerate enough to not let you start entirely from scratch when it comes to catching the Apple-Crab, and she has recently, with Applebloom's help, constructed what she reckons is a pretty fearsome trap for the elusive beastie. It appears to be an extremely large grid of squares, a hundred by a hundred by your count, with several arrows pointing in all different directions, along with walls of several revolving doors.
So how, exactly, does this implausibly elaborate device function, you ask? Applejack proudly explains. The trap is to be baited with several apples, and when the crab attempts to nibble on one, it will instantly activate the device and force the crab to move. The arrows on each of the squares will move the crab in the same direction as that arrow, after which, once the crab has left that square, the arrow will rotate by ninety degrees: if it's pointing north, it will move the crab north and then change its arrow to face east, and then if the crab should visit that same square again, it will be forced to move east, and the square with that arrow will rotate again to face south, and so on.
Such a device is necessary as the Apple-Crab must remain in almost constant motion, lest it gain its bearings long enough to use its venomous and acidic bubbles that they naturally possess to simply melt their way out of the trap and wreak havoc on the orchards once again. The only catch, however, is that in the event that the crab hits an edge square and it points towards the wall of the trap, nothing will happen, and the crab will be able to escape. However, she remains decently confident that such a trap will be for the most part largely unescapable, and her crop shall be saved.
Is she right though, you think. Is this trap actually foolproof, and if not, how is the best way to carefully and deliberately destroy her hopes and dreams?