What does twain say is the symbol for a complete house

A cat.......

"When there was room on the ledge outside of the pots and boxes for a cat, the cat was there--in sunny weather--stretched at full length, asleep and blissful, with her furry belly to the sun and a paw curved over her nose. Then that house was complete, and its contentment and peace were made manifest to the world by this symbol, whose testimony is infallible. A home without a cat--and a well-fed, well-petted and properly revered cat--may be a perfect home, perhaps, but how can it prove title?"