The Green Glass Door is a common word game where you give clues about which belongs behind the green glass door or outside the green glass door. Basically, all the clues will have words that have exactly 2 duplicate letters which belong inside the green glass door.

Some examples:

• Caesious, as cheesey as it might appear, is behind the green glass door while Caesar is left out.
• Behind the door you may attend classes at school or college but not courses at a university.
• Minnie Mouse is in, Mickey Mouse is not.
• Stellar is in, lunar is out, but moon is in and stars are out.
• Buttons and zippers are behind it, snaps aren't.
• flowers may bloom there but they don't grow there.
• Bill and Hillary Clinton may enter but Chelsea has to wait outside.

In a similar vein:

• A stool is behind the green glass door, but a stingray is not.
• Matresses are behind the green glass door, but a scorpion is not.

OK, not the same rule as above. So what is the difference? Hold on, it isn't over yet...

• A Lion (or any kind of cat, for that matter) is behind the green glass door, but the Yellow-Banded Poison Frog won't go near a glass door, ever!
• Beloved lady Shrimp is in, but the Portuguese man-of-war, good sir
• Physalia Physalis himself, in all his splendor and glory, is out.
• Flamingo is in. Corn snake is out.

See the pattern yet? If so, this should fit right in:

• The smiling axolotl is behind the green glass door, the spider is not.
• The octopus is in, the mouse is out.
• The gibbon is in, the gorilla is out.
• Aardvark. Come on, aardvark, for crying out loud! I'm not giving anything more away! Aardvark IS IN! The moose is, naturally, out.

And, the last ones:

• Both Palaces and huts, their differences aside, are in. Skyscrapers are out.
• Bill Clinton is in, Hillary is out.