Step 1: Materials
All you need is two aces and a seven.
I used jokers that I put stickers on them that say this, that, and other, you can make them if you want, but I'm not going to explain now. If you want to know how to make them just ask me and I will send you instructions.
Step 2: Double Lift
Use an entire deck while practicing.
1-Hold the deck like you are dealing the cards out.
2- Grab the first card, while doing this also grab the second card.
3- Flip these cards over, but try to keep them together and not show that you have two cards.
4- After showing the second card, pretending its the top card, flip them back over.
5- Practice until good enough to show.
Step 3: The Glide
2- Slide the bottom card back with your ring finger and pinky finger.
3- Slide out the card second from the bottom pretending its the bottom card.
4- Slide the bottom card back into place.
Step 4: Doing the Trick
1- Now do the the double lift hiding the seven and showing the ace, flip them back over.
2- Spread the cards out showing the back of all three, pull out the middle card (ace), put it back in after showing the audience.
3- Now do the glide hiding the other ace and showing the same ace again, now put the shown ace on the bottom.
Do the same steps that you used showing "this" to show that, this works because "that" is now in "this's" old spot (middle). This tricks people because they think that "this" turned into "that".
Now is the time to show the "other" card. Take the cards out of your hand saving "other" for the last.
You have finished showing the This-N-That trick.