A quick learner

Imagine that household rules are like a line drawn in sand, with the command: "Do not cross here!"
Some children will respond by running as fast as possible over the line. They're the defiant ones. When given a command or request, they respond with screams, yells, or stubborn-faced disobedience.

Then there are the others. The sly ones. These children, when told not to cross the line, will respond by subtly putting their little toe onto the far side. If you don't pick up on this, they'll extend it to their whole foot, then their leg, then slowly inch further into defiance. They can be the negotiators, trying to convince you that the line is not really the line you think it is. Unless you're watching carefully, the disobedience of these ones is easy to miss. After all, when you ask them to not do something and they obey 96%, isn't that close enough?

We have one of each child.
Our daughter, when asked to do something, will often respond with screams and then lie down on the floor in full tantrum. If you ask her to come to you for some reason, she'll often run full pelt in the opposite direction. She's the openly defiant one.

Our son, on the other hand, is more subtle. For example, if you ask him to keep quiet in a public place, he'll make a single, medium-volume cry. Just at the level below which you'd easily reprimand him, but loud enough to obviously be testing the boundary you've just set. If you ask him to come to you for some reason, he'll tell you that he's doing something incredibly important, like cleaning up. When you're an exhausted or distracted parent, it's very easy to miss this sort of thing.

Another thing he's discovered is the benefits of confusion. For example: your son is found during nap time to be up and playing in his room, nappy off. The mother is out, and the father asks, "Why aren't you in bed? Who took off your nappy?" The son replies, "Mummy did it!"

He's only 3.