For the cat cookies with tuna, finely mash the fish (its own juice serves as liquid). Add the remaining ingredients to the fish farce and knead into a smooth dough with about 50 ml of water or cat milk. Cover the dough and let it rest for about half an hour.
Preheat the oven to 180 degrees and roll out the dough thinly. Cut out small cookies with the cookie cutter of your choice. If you do not have a cookie cutter available, simply cut small corners with a knife. Place on the baking sheet lined with parchment paper.
Bake for about fifteen minutes. Let the cat cookies with tuna cool well and dry.