Katie Couric made quite the entrance on The Late Late Show with James Corden when she stopped by to chat with the host on Wednesday. She almost gave James a heart attack after it appeared that she had tumbled down the stairs while trying to fix her heels. The entire studio was silent as James ran from his seat to help Katie, saying, "Are you OK? Wait, wait, wait . . . " — only to realize that it was a stunt double and that Katie had pulled an April Fools' prank on him. James fell to the ground laughing and told Katie it was an amazing prank, but he shared what he was really thinking as he watched her fall. Watch his priceless reaction, then check out why James Corden is killing it as the host of The Late Late Show.