worms have bristles that help them move through the earth. Anyone that has snitched worms off the lawn at night knows that they use these bristles to keep themselves in the ground when you or a bird tries to pull them out.
All fish eating birds and fish swallow fish head first to stop any spines etc catching in their throats so presumably fish would naturally swallow a worm tail first so that the bristles fold down as the the worm goes down the throat.
I tend to put the hook in the head of the worm and when using a worm chopped in half put the bottom half on in the cut bit.