The next episode is called The Variable. The title must be meant as a nod to The Constant, the title of the 4th Season episode where Desmond visited Faraday in Oxford, in 1996, and watched Faraday send his lab mouse “Eloise” on a fatal trip through time.
Here are a couple of very short trailers:
This one ran after Some Like it Hoth. The part for The Variable starts at 0:17
Here’s the 10-second promo that ran after the clip show:
And here is a slideshow of promo photos from the episode, showing our Lostie friends in their Dharma outfits (may be very slightly spoiler-ish):
The Variable will air on Wednesday, April 29, 2009, at 9:00 pm to 10:02 pm (an hour earlier Central).