The spiral showcase that appeared today (5/31) states to feed a pet . Well no credit is given in the progress of the spiral showcase unless one also trains the pet and feeds it a snack. I tried just feeding a snack to a new pet and several different pets I have and no progress was made on the spiral showcase. Progress only showed when I trained and then feed a snack.
"Feed pet a pet snack for happiness" or "Win a Pet game"
You do not necessarily have to win a pet game to get credit for feeding the pet snack. If your wizard has participated in enough of the games to qualify for the "Skip Game" button, the feeding at the end will still give you credit.
I do not know if feeding a pet snack after a loss will give you credit. Perhaps someone else does.