Did you know that Helen Keller had a dog?
Well, neither did she!
Helen Keller's Invisible Dog
Explanation
Explain Bear
Listen up, nugget brain. Helen Keller was blind and deaf, which means she couldn't see or hear. The joke plays on this by suggesting she couldn't even 'have' a dog in the sense of knowing she had one because she couldn't perceive it. Get it now, genius?