Don't Lie to Me, I'm Your Mother!

Here's an excerpt from a few days ago:
"Ari, did you spill chocolate milk on the table?"
"No, Egreck did it."
"I find that hard to believe, Egreck doesn't have opposable thumbs, he's a cat."
"Well he did."
"It's okay if you did it, just tell me. I won't be mad."
"I didn't!"

Here's another one. We're walking down the street and I see one of those chalkboard signs outside of a restaurant that list daily specials. One minute I'm looking at the sign, and the next minute I notice that the once pristine sign has blurred words. Then I see there's chalk residue on Ari's fingers.
"Did you touch that sign?
"No."
"There's chalk on your hands, I think you touched it."
"I didn't!"
"Please just tell me the truth, I won't be mad."
"I touched it."
"Don't do that! The people inside the restaurant will be mad and people walking by won't be able to read the sign!"
"Okay [Sighs]."

I don't understand the lying. It seems like he just doesn't want to get in trouble. The thing is, if he's going to lie, at least come up with a plausible excuse. I don't want to give him any ideas, but if I were him, I would blame everything on Samara. He sort of had the right idea with Egreck, because Egreck can't talk back and say something like:
"No dude, that wasn't me."

But Samara can't talk either...yet. Blame it on the baby, not the cat! If Samara "accidentally" spilled chocolate milk on the table, she can't help it. I would totally milk that for all it's worth, pun intended. But, again, I don't want to give him any ideas.

Seriously though, this lying situation is grating on my nerves. I wish he would just cop to what he did instead of making things up.

Did your kid go through this phase?