When you press the Delete button on the Patients|Information screen, a confirmation window will appear.
If the pet cannot be deleted because it is in use (normally because it has an owner), the text will be "xxxx has relationships and cannot be deleted. Do you want to deactivate it instead?"(where xxx is the name of the pet you are trying to delete). Pressing OK will unset its Active flag, Cancel will abort.
If it is in use but can be deleted (because it has no owner), the text will be "xxxx has relationships. Are you sure want to delete? This operation cannot be undone." (where xxx is the name of the pet you are trying to delete). Pressing OK will delete the pet as well as all references to it, Cancel will abort.
If the pet is not in use and can be deleted, the window will simply ask you to confirm the delete. Press OK to confirm or Cancel to abort. (This will only occur if the pet has no breed, taxes, discounts, etc set.)