Foie gras production involves force-feeding ducks and geese to engorge their livers. The practice is banned in the UK and several other countries as incompatible with humane treatment of animals.
Foie gras production deliberately causes pathological organ enlargement through a process that birds actively resist and find aversive. The birds cannot walk normally by the end of the force-feeding period, and respiratory distress from the enlarged liver is common. The practice is widely regarded by veterinarians and welfare scientists as fundamentally incompatible with acceptable animal welfare standards, which is why production is banned in the UK.