DOF (Depth of Field)

I do have a general understanding of how manipulating aperture and/or focal length will alter the amount of DoF.

So far this knowledge has served me well until this picture below:

I don't know why the subject's left foot is out of focus but not the right.

The distance of either foot to my camera should be nearly equal and I expect both to be either in or out of focus.

I am stumped, what do you think happened here?

Difficult one as can't quite figure out the perspective. Just a guess and if you look at the right wing tip of the bird, that appears to be a point at the circle of confusion. A slight angle with the branch from left to right (as looking at it in the photo) with the right just a little further away than the left than it is entering the circle.

Either that or you got your finger on the lens. <just kidding>