You are going to find all kinds of novelty cards here and they will be shown in no particular order.
MECHANICAL CARDS
There are many types of mechanical cards. These cards generally have hidden images that you have to flip open, or pull out to see. The first three cards are the type you have to pull out. As you pull the tab out 12 smaller cards are flipped over one by one. The smaller cards in the third card are in color.
The next four cards demonstrate the type of mechanical card where you have to flip it open to see the smaller images inside. The first two cards show 12 images about the same size as the image on the front. The next card shows the front and, next to it, 1/2 of the inside showing the smaller 24 images attached accordion style. The last card has 14 images under the heart. Unfortunately I can't show any of these smaller images without damaging them.
With this card you flip up the bottom half and you see the 2nd image which is where you would write your message. You then opened up the bottom half and 12 images would fan out accordion style as seen in the 3rd image. There is a string or ribbon missing that would have been tied using the 2 holes thus keeping the card closed when mailed.
This card has 12 images that you can remove completely from the main body. There are 6 images on each side.
This rather worn out push-pull tab card makes the piano player move as if he is playing the piano. Made by The Cincinnati Credit Clothing Co. 15th. & Broad St.
This second push-pull tab card, put out by the Flach Bros. Grocery Co. on the corner of 2nd & Vine St., changes faces when activated. Apparently if the person with the card matched a face with one that was probably hung in the grocery store they would win some kind of prize.
Using the same technology as the above 2 cards, this Deeks puzzle card shows two scenes when tilted from side to side. Fountain Sq. & City Hall.
I got curious one day and opened the envelope on the card on the left to see what was written. There is a piece of paper that just says April 1st.
MINIATURE CARDS
The first two items were produced by the Kraemer Postcard Co. They both contain 20 2 1/4" x 3 1/2" miniature cards, the top one in color and the one below in black & white. I have spread out the box above (pretend the white portions are black) to show you what they look like.
The packet above was Published by the Grogan Photo Co., Danville, Illinois. The 20 miniature photographs are 1 3/4" x 2 3/4". It is dated 5/1/45.
The 12 2 1/2" x 3 1/2" black and white photographs were Published by the Wittenborg Toy Co.
Kraemer collectors will be interested in the three cards above. The last card shows the back of one of the cards showing the thin piece of paper, with the normal Kraemer layout, pasted to the card (somewhat crookedly). The person put their photo in the oval and pasted this paper over it.
DIFFERENT MATERIALS USED FOR POSTCARDS
ALUMINUM CARDS
These cards are entirely constructed of aluminum which ,as you can see, makes them very hard to keep flat. I show the back of one of these cards to bring up a point I should have mentioned before this. Very popular was the use of clear or glassine envelopes where you can see the card inside. As you can see on the back of these cards that was how these were meant to be sent. You put the address and message on the card but you put the stamp on the glassine envelope. The last 3 images are different from the others in that they were meant to be mailed in the normal way. I show the back of one of them. The stamp is missing and since it was mailed normally there are postal markings on both the front and back plus writing. I had to do a lot of retouching to make it look presentable thus it may look a little TOO good.

Same view - Different
perspective
COPPER

Cincinnati Union
Terminal
Fountain Square
Copper cards do not scan very well especially since they are also embossed
METAL CAR ATTACHED
POSTCARDS IN A NUT SHELL
This plastic nut shell was mailed just like the first image shows, the two halves snapped closed for mailing. It was produced in the early 50's.