I think you can often tell when someone is lying by their body language. For example, they might avoid making eye contact or fidget a lot. Sometimes, their facial expressions don't match what they're saying, like a forced smile. Also, if they pause a lot or hesitate when speaking, it might mean they're not being truthful. Watching how they move or change their posture can also give you clues.

When someone is lying, their story might not be consistent. They could change details over time, or their explanation might not make sense. Sometimes, what they say doesn't match what they do, or it contradicts known facts. If their story is overly detailed or complicated, it might be a sign they're trying to cover something up.

Behavioral changes can also signal when someone is lying. They might become defensive or aggressive if questioned. Sometimes, they offer elaborate excuses or justifications. Physical signs like excessive sweating or changes in voice pitch can be telling. On the other hand, they might seem unusually calm or unemotional in serious situations, or they might avoid certain topics altogether.