1.  Both take up too much space on the bed.
2.  Both have irrational fears about vacuum cleaning.
3.  Both are threatened by their own kind.
4.  Both like to chew wood.
5.  Both mark their territory.
6.  Both are bad at asking you questions.
7.  Neither tells you what's bothering them.
8.  Both tend to smell riper with age.
9.  The smaller ones tend to be more nervous.
10. Neither does any dishes.
11. Neither of them notice when you get your hair cut.
12. Both like dominance games.
13. Both are suspicious of the postman.
14. Neither knows how to talk on the telephone.
15. Neither understands what you see in cats.