How do you know if someone is lying to you or not?

If someone is lying, you may notice a slight change of voice. If you are having a conversation, if they are lying, they will tilt their head and look to the upper left, as if recalling something. They may stammer, or croak, along the lines of that. or they can never look you in the eyes and if they do they doint look for long they keep there eyes on sumthing else . sometimes you can come back to the person at aanother time to see if they say the exzact answer later . it works all the time!