world of pajama

Some few nights ago I was lying in bed feeding D. and contemplating his pajamas. They have a picture of a cat and, behind it, an outline of another cat. In my sleepy stupor, P. and I had a conversation that went something like

z: Is this supposed to be two different cats? or is it two pictures of the same cat?

p: It's two pictures of the same cat.

z: But in the world of the pajama, is there one "real" cat and one drawing of that same cat? or is this one cat having an out of body experience?

I can't remember exactly how the rest of the conversation went, but the phrase "in the world of the pajama" had us snickering for the rest of it. Who talks like this? And does it sound just as silly when I use similar phrases in class?