A person's face holds no polygraph. Decades of testing single tells against real lies has turned up almost nothing you could bet on by itself. What lying does do is add work: the person has to invent, keep the invention consistent, watch your reaction, and manage their own nerves, all at once. That extra load leaks in a few predictable places. None of them is proof. Together, and set against what you already know about the person, they tell you where to look harder.
Lying is mostly a load problem
Made-up answers tend to be thinner than real ones. A true account carries texture the speaker is not managing: the weather, a smell, who else was in the room, a boring aside. An invented one delivers the main claim and little around it. Over-explaining is the same load seen from the other side, an answer arriving with justifications nobody asked for, because the speaker is selling it rather than reporting it. A short delay before answering, or your own question handed back to you ("did I call him back?"), is time being bought.
The detail test
Ask a small, off-center question about something inside the account. Not "are you sure," which invites a flat yes, but "who got there first" or "what did you order." A true memory produces the side detail with no effort, sometimes with a correction. A constructed one tends to stall, go vague, or bristle that you asked. People rehearse the plot, not the extras. The interview version of this, where the gap between a smooth answer and a stumbling detail does the work, is laid out in the pause told her everything.
Stress shows, and so do nerves
Under pressure the voice can climb a little, especially on the key word. Hands move to the face and neck. The normal rate of fidgeting changes. All of that is real, and all of it also happens to an honest person who feels accused, is running late, or dislikes the subject. Without a sense of how this particular person acts when nothing is wrong, a rise in pitch is noise, not signal. Read something neutral first, then bring in the hard question.
The signs that do not work
Looking away is not a lie sign. People break eye contact to think, and anyone who has heard the myth will hold your gaze harder while lying, not less. A single gesture, however textbook, is not evidence. The mouth-only smile is a fair exception to know, because the eye muscles that crease a real one are hard to fire on purpose, and that detail alongside the rest of the face is covered in the seven emotions you can read on any face.
Stop scanning, start probing
Watching for tells keeps you a step behind. Making the lie harder to hold puts you ahead. Ask for the account out of order, the end of the evening before the start. Repeat back a small, wrong version of what they said and see whether they correct it firmly or let it pass, since people defend an accurate picture of themselves and tend to leave a convenient error alone. After a vague answer, stop talking and wait; the one who breaks the silence often fills it with the part they meant to hold back. The Reader turns moves like these into a set method for drawing out the truth without an accusation.
A wrong read costs more than a missed lie
Treat every one of these as a question, never a verdict. Deciding someone lied when they did not does lasting damage, and it is an easy mistake to make when you have gone in expecting deception. Line the signals up, weigh them against the person's normal, and hold the conclusion loosely. To see your own behavior under pressure, the free DISC test takes about two minutes.