But transplanting pig cells into people is still controversial, since it brings the risk of transplanting pig diseases (which may be contagious) at the same time.
While the beneficial results in pig hearts were particularly important due to their resemblance to human ones, two challenges remain before the same technique can be safely attempted in people.
Developers with a particular way of designing houses design the same houses over and over again and the result is "ugly rubbish" or "pig ugly" buildings in Nick Boles' opinion.
Alan Reilly, the chief executive of the Irish food authority, said there was a "plausible explanation" for the pig meat finding its way into the burgers, since meat from different animals is processed at the same plants.