Cats' and dogs' behaviour toward each other after seeing behaviour that has opposite meaning in the two species indicated that they understood the behaviour of the other species. Eighty percent of the opposite meaning behaviour by a dog was responded to by the cat in a dog-appropriate way and 75% of the opposite meaning behaviour by the cat was responded to in a cat-appropriate manner by the dog.
The Domestic Cat: The Biology of Its Behaviour, 3rd edition, edited by Dennis C. Turner and Patrick Bateson
Ooh, inter-species (ETA: cross-species - I blame "Friday brain") communication! I may have to hunt down the study cited in this paragraph.
This is kind of dry for my tastes, to put it mildly. It'd probably go down easier if I just read bits and pieces of it here and there, so I might check it out from my library sometime.