"The dog marks its food."
Translation:Hunden afmærker sin mad.
It should probably be accepted.
Kathy, it's probably something between "It's not in the database yet" and "It misses the intent of the sentence." Since the dog is most likely marking its own food, the reflexive sin is used here. Dens usually implies that the dog is marking the food belonging to something else (or to some other animal).