Polygraphs are inadmissible in court because they are inaccurate, have false positives and can be fooled into giving false negatives as well.
They are all but useless except in the discovery or detective phase of an investigation.
All true, but missing the bigger picture. HTF do you get that many trained polygraph people to spend that much time with that many witnesses?
Have it on a big screen above their head with a Pinocchio animation
You offer them milk and cookies. Or waffles. Tell the truth now, who can resist waffles?
I'd lie and tell them I was a polygraph expert just to get free waffles. And if they put me on a lie detector to confirm I'd tell them I passed because I'm a polygraph expert and they don't know how to results without me.
Because...
a) Polygraphs aren't admissible in court
b) Polygraphs aren't terribly accurate. Many people can fool them.