I really hope the Sense Motive (3e) / Insight (4e) skill doesn't make it into 5e. I think it clobbers the heck out of roleplaying and common sense when PCs can just ask "is he telling the truth?" and roll a d20 and find out the answer.
(Yes, even if the DM makes the roll instead of the PC, it's still a really dumb mechanic that's stupidly harmful to roleplaying and plot development.)
If you wanna think a guy is lying, then sure, think that. Come up with a reason he's lying. Prove him wrong on something, call him out. But let's drop the idea that everyone has a fair-to-good chance to measure someone's heart rate and sweaty palms and instantly tell who is deceitful.
(Yes, even if the DM makes the roll instead of the PC, it's still a really dumb mechanic that's stupidly harmful to roleplaying and plot development.)
If you wanna think a guy is lying, then sure, think that. Come up with a reason he's lying. Prove him wrong on something, call him out. But let's drop the idea that everyone has a fair-to-good chance to measure someone's heart rate and sweaty palms and instantly tell who is deceitful.