Math Joke

ех=е^х
ex and a constant were walking down the street. Suddenly, the constant notices a differential operator walking along the other side of the street. "Oh, no!" exclaims the constant. "I've got to run away! You've got to hide me! There's a differential operator... he could reduce me to nothing!" "Hmmmph," came the haughty reply. "I'm ex. He can't do anything to me." So ex walked across the street and introduced himself. "Hi. How are you doing? I am ex," he bragged. "Pleased to meet you," replied the differential operator. "I'm d/dy."

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After the flood Noah tells the animals to go forth and multiply and repopulate the planet. A week later he visits them to see how they're doing and they all have little cubs or whatever running round at their feet except for 2 snakes.
So Noah asks them why they aren't multiply to which the snakes reply they need a Noah to cut down a tree so that they can.
So Noah cuts down the tree and a week later returns to find lots of little baby snakes so he asks the snakes why they needed him to cut down the tree.
The snake replied: We're adders we need logs to multiply.

A cat has nine tails.

Proof. No cat has eight tails. Since one cat has one more tail than no cat, it must have nine tails.