Lucy is gradually learning the things she is not allowed to play with. She lacks, however, the self-control to actually leave those things alone.
Every so often, when I'm busy with Linus and she has wandered off behind me for a moment (if she's out of sight for more than a minute or two, I go to see what she's up to -- usually she quickly reappears), I'll hear her saying "No ... no ... no ... no ... no ..."
When I get close enough to see what she is doing, I invariably discover that Lucy is holding something she is not allowed to play with. She generally relinquishes the object without too much fuss.
"That's right, Lucy. No."