As Pets spend time following their masters, their Hunger value slowly goes down.
When it reaches 0, the pet returns to the player's inventory at a massive loss of closeness.
Once it reaches 50, the pet will begin to mope and show signs of weakness.
This can get the owner in trouble with other players, if they see it going on. Often the owner will be defamed for allowing this to occur. While starvation is one of the problems with owning a pet, overfeeding it is another. It gains 1 point of closeness when fed, so sometimes new pet owners will continually feed their pet. This will actually cause the closeness to decrease as well. Pet food can be purchased for 30 mesos from special pet food sellers, which can be found in Mu Lung, Ludibrium, Orbis, Leafre, and Henesys.