First you see the crochet piece in it's finished, but in un-detailed form. This being a sheep's arm, in need of a single long stitch to give the appearance of a grooved hoof.
With contrasting color, insert the crafting needle through one side of the hoof, and exit the opposite side, as seen in the photos below.
Bring your yarn around the front of the piece and re-enter the hoof in the same stitch as you originally added the contrasting color, and follow the same stitch path again - seen below.
Slowly, evenly - begin to pull the ends tightly until you have the long stitch tight against the foot - be careful not to pull too tightly as it is very possible to either brake the yarn you are working with, or break stitches within your project. An even, constant tension and patience works best.
Once you have the desired look, you want to re-insert the needle, slightly to the left or the right of the exit stitch, so that both tails are on the same side and you can make a knot to finish off as seen below.
After knotting, snip off your remaining tails of yarn, and hide the small remain inside your work, for a finished/polish end product. I have a pair of needle nose tweezers, but almost any slender item will work to hide those tail snippets.
And Viola, a hoof.
Please keep in mind that this was a very quick tutorial, and I know that the photographs are not the best quality, it is merely an intent to get the idea.
If you have multiple toes, repeat the process for as many 'separations' are needed.