Here are a few ways to tell if someone is lying:
How is the person talking?
If you know how the person usually talks, notice any change in speed. Is he talking faster, a lot slower, noticeably pausing, or even taking a long time to answer?
Look for any change from the baseline norm he usually is at
Is the person almost frozen?
When people lie they will sometimes freeze and turn slightly away from the person they are talking to.
*Note some people might start moving a lot to pretend to be truthful. So during your analysis look for changes from the norm
Is the person making eye-contact?
To tell if someone is lying always look at the persons eyes. People have a very hard time making eye contact when they are lying and this is an almost sure-fire give away.
Is the person giving off stress signals?
Whenever you lie your body reacts automatically, and gives off particular behaviours.
Is the suspected person scratching, itching, swallowing or rapidly blinking? Is the person fidgety (tapping his foot, rubbing his fingers etc.)?
If yes, this behaviour shows that the person is uncomfortable and is most likely lying.
In which direction is the person looking?
Looking to the right stimulates the left side of your brain; the side responsible for creativity and imagination.
So if the suspected person is looking to the right he/she is stimulating their creativity and making stuff up.
Likewise if the person is looking up and to the left, they are using the right side of their brain. This side connected to memory and therefore the person might be recalling something.
In the end, it’s up to you to decide whether someone is truthful or not. All people are different and for an outsider, it is quite difficult to determine if someone is lying. So if you know what the person is usually like you will have an easier time distinguishing between normal and odd behaviour.
Note: It’s not always the best thing to openly accuse somebody. Try to make sure and then privately talk to the person about it.