Normally for me it´s absolutely clear, that chinchillas should be paired up, because in their natural environment they live togehter in clans. So they should even "in prison" get another chinchilla to play with. Having just one chinchilla is only acceptable for me if you spent DAILY a lot of hours together with your little friend. It´s not acceptable to keep chinchillas together with other pets, e.g. birds, guinea pigs, hamsters or rabbits. Birds, guinea pigs and rabbits are different to chinchillas dayactive, so that they would disturb the chinchilla´s sleep during the day as the chinchilla would disturb them during the night. If you put a chinchilla together with a rabbit or a guinea pig in a cage the chinchilla could jump to higher sitting-boards which the others couldn´t reach, but among the different sleeping times there would also be a problem with the food. A chinchilla should not eat rabbit´s or guinea pig´s food because this is much to substantial and the chinchilla would get constipation. Hamsters have the same living-rhythm as chinchillas, but they are real loners so that there problems would appear. If you want to give your chinchilla a friend you should give him another chinchilla. The best would anyhow be to pair up the chinchillas from the beginning on.