Well, we all have our little blind spots. And usually, these blind spots relate to our friends or loved ones. Dr. Cal Lightman (Tim Roth) is an expert at uncovering the truth and decoding the body language of others. But it turns out that he's not so good at this when it comes to his own daughter.

On the season finale of 'Lie to Me' (Mon., 9PM ET on Fox), Lightman arrives home to find his teenager daughter Emily (Hayley McFarland) messing around with a boy upstairs. Cal is outraged, and forces the young man (played by Carter Jenkins) to leave. Emily is pretty upset herself, and says this to her father: "It's just sex, dad!" Which really doesn't improve the situation.

Now, Lightman is forced to have an intensely awkward "sex talk" with Emily. "Look, give me a break, all right?" Cal says when his daughter rolls her eyes at him. "I'm making this up as I go along." However, the sex talk proves to be highly unnecessary -- as Emily didn't have sex with the boy. She just claimed that she had in order to upset her dad. What a relief! Even though this means that Dr. Lightman -- who is supposed to be a master of exposing deceit -- has been tricked by his own offspring.

"So that's the good news," Emily tells Cal. She didn't "do it" with the boy upstairs. And the bad news? She's already had sex -- two boyfriends ago. Whoops! So Lightman has been fooled twice by his daughter. This whole parenting business is harder than it looks, even if you are a professional lie-detector.