At Agile Fusion, Michael Feathers demonstrated a technique he learned from Ron Jefferies, that Ron called Ironman CRC. While at Agile Fusion, a few of us used the term Naked CRC, which I think is much better as it is more memorable and better describes the technique.

This is really hard to describe unfortunately. It is much easier to demonstrate. The idea is that you layout index cards, without anything written on them, as you describe basic collaborations of the system. The cards serve as a visual guide to your discussion. The key idea is that you only focus on a few classes / objects in the collaboration. Besides making the discussion easier to follow, using only a few classes allows people to follow the significance of the cards, as they have nothing written on them. I like this because it forces me to keep things simple when I use Naked CRC. If someone tells me "Wait, what kind of object is this card?", I realize that I have probably over complicated the example.

I have modified the technique to use multi-colored index cards. I bought a pack of index cards that came in four colors. (Incidentally, in college I learned about four color maps and how four colors is actually sufficient to draw any map without having any two adjacent entities be the same color. So, four colors works well with Naked CRC). I find the colors are easier for people to keep track of the model being shown, without resorting to writing on the cards and making things too complicated.