The game is no -limit hold'em. Your rival in early position raises pre-flop, you call. It's just you and him. He then declares that he "checks in the dark." No, don't motion for that light switch, he is giving you free information. He is checking the flop before viewing the cards, thereby putting the "first" action on you and, if you also check, forgoes this betting round.
So what does this mean? Well, it could mean he has a good hand with little room to improve, so he doubts any new cards will better his hand. In this case, an assumption of a pocket pair is fair and any reraise or sudden confidence on his part probably means that you are up against trips.
It could also mean he doesn't know how to play you well and merely doesn't want to be faced with a decision.
As I see it, there are two advantages of a "check in the dark" heads-up and he is probably hoping for one or the other. Firstly, he wants to check the flop down and thinks it is more likely for you to check if he checks without knowledge of the flop. Secondly, he wants the advantage of late position and is willing to risk a betting round to get it.
This tactic is important to consider if you play anywhere off-line, as it does come up from time to time. If it happens to you, never fear. You have just been given more control of the game. If you are so inclined to "check in the dark" yourself, be cautious of who you are playing. As a general rule, giving out information for free is a no no in poker. However, against the easily rattled, the psychological gain from the move can pay off.
What say you? What do you think your opponent is pining for with a blind check?