A lecture about English
A linguistics professor was lecturing to his English class one day. "In English," he said, "A double negative forms a positive. In some languages, though, such as Russian, a double negative is still a negative. However, there is no language wherein a double positive can form a negative."

A voice from the back of the room piped up, "Yeah, right."

A very interesting fact
Doctor: Did you know that there are more than 1,000 bones in the human body?

Larry: Shhh, doctor! There are three dogs outside in the waiting room!