Looking closely at the artwork above you'll notice the images are all created with straight lines. Printing with a cardboard tool is always a fun challenge. The simplicity is what makes it so open to diversity. It's wonderfully open-ended as the student may begin with a particular idea and it develops into another or the student may have no idea in mind and just start printing to find their mind making connections to create an image.
Other variations of this idea and the process can be seen here.