S6, E7: Pressured by her lawyer Will (Eric McCormack), Karen (Megan Mullally) decides it's time for her annual Walker corporate physical, but begins to regret this decision after being examined by a slightly unorthodox physician (guest star Jack Black, "School of Rock"). Elsewhere, while accompanying Karen to her physical, Jack (Sean Hayes) finds his true calling - student nursing - and begs Will to support this new endeavor or face his eternal scorn. Debra Messing also stars.