My thought was that monsters only knew of what you'd actually affected them with so far, not whatever might happen to them in the future due to a power. In other words, Dance of Death doesn't grant the target a prophetic glimpse into the future.
So I was going to argue this on the basis of pure common sense spirit of the rules. But then I went back and re-read the page 57 quote in the Player's Handbook that everyone has been using as though it said, "Using a power on a monster allows that monster to know exactly what you're having for breakfast tomorrow."
Let's read it a bit more carefully, because I was thrilled to discover that it says exactly what I thought should be the case:
"Whenever you affect a creature with a power, that creature knows exactly what you’ve done to it and what conditions you’ve imposed."
Oh, this is lovely. It knows two things:
1) What you've done to it. Not what you're going to do. What actual damage or active effects you've hit it with so far. If you've imposed ongoing damage, or debuffed it, or applied any condition, the monster knows it.
2) What conditions you've imposed. Condition is a specific word with a specific game meaning. Conditions are listed on page 277, and Marked IS one of them. But "subject to some other future harm because of a power" is NOT.
Whatever subsequent things that your power might allow you to do in response to the monster's actions are not something you've "done to it" nor a "condition" imposed on it.
If this wasn't the case, any power related to tricking a monster into doing something would be entirely useless, as your clever trickery could never fool so much as a braindamaged ogre.
But fortunately, the rules and reason align once read carefully. No omniscient gelatinous cubes cunningly evading your masterful tactical tricks anymore!