After a week off, Bill Maher should be fresh and feisty – and tonight, his show features two of its most talkative, provocative and entertaining frequent guests. One is Neil deGrasse Tyson (at left), a frequent fixture on PBS science shows as well, who has a formidable gift of getting to the heart of complicated subjects and explaining them simply. Another is James Carville, who, especially in front of a live audience, loves to poke the bear and say volatile things.