Complex sentence: The flea is given to the czar, to whom Lefty explains that he needs to look closer and closer at the flea to see what they've done after he winds it up and finds that it doesn't move.
Split into simpler sentences: The flea is given to the czar, to whom Lefty explains that he needs to look closer and closer at the flea to see what they have achieved. He winds it up and finds that it doesn't move.