For those stuck in the cave puzzle with the snake and naked Clare, do NOT panic! After a few tries the game will remove the snake to make it easier but this prohibits you to reset the screen if you messed up. Do not push a rock on the pressure plate, this will not work.
Make a new save game, then reload it. This will reset the puzzle. Then push the leftmost rock so that the sanke is trapped. Then just walk on the pressure plate AND PRESS ENTER. Then a second pressure plate will appear. Do the same and you can proceed to the next room to the right.
Hope this helps, this is not mentioned at all in the walkthroughs.