Philosopher Peter Singer opens the argument that has shaped decades of animal rights debate: if animals can suffer, their interests deserve moral weight alongside our own, drawn from his utilitarian framework built at Princeton. Animal welfare researcher Sara Hintze, filmed in her lab at the University of Natural Resources and Life Sciences in Vienna, runs psychological experiments on young fattening pigs that reveal surprisingly human-like emotional responses. Evolutionary biologist Jon Mallatt pushes the question back 500 million years, tracing when and why nervous systems capable of feeling anything at all first appeared, and where that leaves plants. The film's counterweight is Dan Shahar, one of the few philosophers willing to mount an ethical defense of eating meat, who argues without denying what factory farming actually involves. Animations translate the thought experiments into clear visual terms throughout. Part of DW's five-part 'Great Meat Debate' series, this episode stays focused on the philosophical core: what obligations, if any, follow from accepting that an animal can suffer.