It's a tradition that began in Germany - one in which JC has never taken part. The others know why. When they first discovered JC's aversion to needles, they teased him constantly. Eventually, it became just another part of JC that they accepted and loved.
When the five of them gather in the studio after so many months, JC waves them over, promising a surprise. He knows they expect a new song, but he pulls up the sleeve on his left arm and holds it out for the other four to see. There's one word there, still red and healing.