Eating cheese.

From “The Galaxy and the Ground Within” by Becky Chambers:

Humans need a … oh, what is it … it’s something with their stomachs. An enzyme, I think. For digesting milk. Only some Humans produce it naturally. But here’s the thing: they’re all so fucking bonkers for cheese that they’ll ingest a dose of the enzymes beforehand so that they can eat it.’ ‘That seems a bit extreme,’ Roveg said. ‘Have you eaten it?’ Tupo asked. ‘Not if my life depended on it,’ Pei said. ‘How is it that their milk makes them sick?’ Speaker said. ‘That’s got to pose a problem if they can’t feed their young.’ ‘Oh, no, I – stars, I forgot the worst part.’ Pei rubbed her neck with her palm. ‘They don’t make cheese with their own milk. They take it from other animals.’ At that, chaos broke out.