What is the difference between oxygen and carbon dioxide

My cat and my dog like best friends

What is implied in this sentence from mark twain's "the £1,000,000 bank-note"? i was puzzled, and wanted to discuss the matter a little further, but they didn't; so i took my leave, feeling hurt and insulted to be made the butt of what was apparently some kind of a practical joke, and yet obliged to put up with it, not being in circumstances to resent affronts from rich and strong folk.

Which sentence is punctuated correctly?  a. under a microscope; the organisms look a bit like ruffled tennis balls they have armored plates that fit together to make a round shape. b. when the water is disturbed; the organisms respond by glowing this makes swimmers look like floating beams of blue light. c. there is a bay in puerto rico that seems to light up at night; the light comes from tiny organisms in the water. d. the luminescence attracts visitors from around the world people are curious to see; this beautiful otherworldly sight.