I've noticed some things about the game which are as follows:
1) Grass has other uses other than for dogs to pee and play in it. If you have enough ownership points then your dogs will find hidden presents in the grass!
2) Cats love the 'Bell Ball' toy, but dogs are scared of it. The same goes for the 2 cat wands.
3) Both cats and dogs like the following toys: 'Balloon', 'Bubbles', 'Miss Chickie', 'Mr Froggins', 'Sir Nibbles' and all of the records.
4) Dogs and cats can do special things if you play records (you can buy these from all the supply stores) for instance, if you play 'Classics 2' your pets do a dance routine (your pets dance better if they have more ownership points) and if you play 'Classics 4' your pets run in circles lots!