Kosher supervision is a substantial industry and an unusual instance of religious law operating inside modern food manufacturing.
Certification is issued by agencies that inspect ingredients, equipment and process, and their symbols appear on a very large share of packaged food in the United States. The difficulty is industrial rather than culinary: emulsifiers, enzymes, gelatine, flavourings and processing aids all require tracing to source, and a line used for dairy production cannot simply be switched to meat. The certification market is competitive, agencies differ in stringency, and consumers who are not Jewish, Muslims, vegetarians and people managing allergies, make up a large part of the demand.
Shechita, the method of slaughter, is where kashrut meets the law of the state. It requires a single continuous cut across the throat with an exceptionally sharp blade free of any nick, performed by a trained and licensed slaughterer, and the animal must not be stunned beforehand, because the law requires it to be healthy and intact at the moment of slaughter. Islamic dhabihah is similar in principle, and in several countries the two are regulated together.
A number of European countries now ban slaughter without prior stunning on animal welfare grounds, among them Sweden, Norway, Switzerland, Denmark and Slovenia, along with the Belgian regions of Flanders and Wallonia, whose bans were upheld by the Court of Justice of the European Union in 2020. Jewish and Muslim organisations oppose these as restrictions on religious practice, and point out that some historical versions of such laws were not primarily about animals at all. Veterinary opinion on whether the method causes greater suffering is divided rather than settled. Both of those statements are true and both belong in any honest account.