Both take up too much space on the bed.
Both have irrational fears about vacuum cleaning.
Both mark their territory.
Neither tells you whats bothering them.
The smaller ones tend to be more nervous.
Both have an inordinate fascination with womens crotches.
Neither does any dishes.
Both fart shamelessly.
Neither of them notice when you get your hair cut.
Both like dominance games.
Both are suspicious of the postman.
Neither understands what you see in cats.