Our Guinea Pig, Wally, has been very depressed since his buddy Gobo passed away in December. I have moved him into the living room so he can have more interaction with us, but he still seems quite sad. Getting another pig is not an option- Wally is older now, and the last of 4, and when he is gone we will not have more guinea pigs. I want his senior years to be good ones. What are some things we can do for him that will be fun, make him happy, get him moving etc?