I knew this was true of humans, but it seems to be true of at least one dog.
Kateva, our dog, is near the end of her life. She’s a decent age (14y4m) with liver disease, a lung mass, and arthritis. No more health food for her. Kibble with ice cream, white chicken over chicken broth flavored kibble warmed in the wave … she eats like a Queen. Alas, you can out-eat exercise, but you can’t out-eat cachexia.
Sam, a guest, is younger and healthier. He’s still on kibble. Which he normally eats — but not when Kateva is getting gourmet food. Then he goes on strike.
Add a bit of ice cream and he devours everything.
Dogs also value fairness.