One way of reading this story is to see in it a convention that if you
borrowed someone's pot, you ought to return it with some food in it as

This gains some strength from the other saying found in both poems; that
coal is the due of a blacksmith.

The law texts specifically state that a blacksmith should charge one
ounce of silver for producing a vessel made from six ounces of iron. But
in addition to this fee, the customer had also to supply, or pay for,
the iron. That is, for the raw materials. (Query whether this might also
have included the coal used up in the process?)

So what if the customer only wanted something repaired? Perhaps the fee
that was charged was net of a requirement that the customer also make
good the coal that was used up in firing the forge?

At any rate, it is possible to see both the bones and the coal as
appropriate forms of recompense for a benefit bestowed by the owner of
the cauldron or the smith respectively.

This might tie in very nicely with the Colum Cille 'copyright' story,
which may be incorporated into our poem. The suggestion being that if
you take someone's book and transcribe it, something in the way of a
royalty ought to be paid.