Make sure you have at least 47 cards before trying to find this card.
In the Debug World, go RIGHT, UP, LEFT, LEFT, LEFT, DOWN. Sweep the dust to follow the "river" through a series of puzzles.
Once you reach the room where the river ends and you must jump between platforms, make sure you grab the dust because you will need it to reach the next room, and finally the chest that contains Card 40!Flow DOWN to reach a new area of DEBUG and hit the Save point. You are now in the same location in the instructions to Secret 7, Secret 8, Secret 9, and Secret 13 .
"Seening as you've gotten to this point, you must be quite Intrasting." (sic)