DEAR DR. FOX: I would like to thank you for your reply to my questions about our cat, Dusty, crying to go outside all the time. I was told repeatedly that every cat I inquired about would not be comfortable sharing a home with another cat. As I emphasize in my book “Cat Body, Cat Mind,” most cats do quickly learn to enjoy each other’s company, as you so clearly witnessed. Two cats living together are generally happier and healthier than those who never have any contact with their own kind. DEAR DR. FOX: Regarding your proposal of an “Environmental U.N”: It is difficult for people to receive the good news of the accomplishments of the United Nations these days.