Proof that all dogs are male:

1. Dogs, like men, are completely predictable.

2. They are supremely interested in your nether regions and pathetically unable to hide this fact.

3. They don't respond when you shout in their ear, but they can hear the sound of a packet containing something consumable being opened a kilometer away.

4. If you once let them hog your sofa, they will feel like they own it.

5. They eat anything. Their basic philosophy is put stuff in their mouths first, ask questions later.

6. They are intensely loyal but sometimes stray through sheer stupidity.

7. When they are not happy, they don’t say anything, but sulk and growl and knock things over.

8. They emit large amounts of gas from both ends.

9. They often consume ill-advised items until they are sick, give you a sad "never again" look, and then do the same thing again the next day.

 
Proof that all cats are female:

1. They are completely unpredictable.

2. They expect to be worshipped all the time.

3. They look cute but are surprisingly tough-minded creatures who make all the decisions.

4. You can call them, but you never know if they will actually turn up.

6. They completely ignore you when you come home.

7. They take the stance that you exist solely to ensure their happiness.

Swiped from The Curious Diary of Mr Jam