Vanna White, Ken Jennings and Mayim Bialik - S3.E14

Contestants go head-to-head for charity in the Ultimate Host Night, with Vanna White calling letters instead of revealing them (for St. Jude Children's Research Hospital) against "Jeopardy!" hosts Ken Jennings (for the Equal Justice Initiative) and Mayim Bialik (for the Mental Wealth Alliance).