Why do we all pat the bone from the nursery rhyme the farmers in his den?

Patting the bone must have been a superstition like Knocking on Wood. Possibly a fossil like those cow skulls you find in the West. Touching a religious relic was a spiritual thing, cross my heart... and so on. That's my guess. I think this was edited out of later versions - I can't recall this verse, the Nurse takes the Child, sure, but patting the bone sounds religious relic-like and it may then have been edited out.

As far as I'm aware patting the bone has never been edited out, everyone I asked remembered that line from the rhyme best. I think the answer to why do we pat the bone is that we just do.

The Farmer's in his Den
The farmer's in his den, the farmer's in his den.
Ee-i, ee-i, the farmer's in his den.

The farmer wants a wife, the farmers wants a wife.
Ee-i, ee-i, the farmer wants a wife.

The wife wants a child, the wife wants a child.
Ee-i, ee-i, the wife wants a child.

The child wants a nurse, the child wants a nurse.
Ee-i, ee-i, the child wants a nurse.

The nurse wants a dog, the nurse wants a dog.
Ee-i, ee-i, the nurse wants a dog.

The dog wants a bone, the dog wants a bone.
Ee-i, ee-i, the dog wants a bone.

We all pat the bone, we all pat the bone.
Ee-i, ee-i, we all pat the bone.