I received a government polygraph test over a year ago.
A mock interrogation would not be very effective. The most important
aspect of a polygraph is leverage. There has to be an incentive for the
person being questioned (e.g. they want an out for committing a crime)
so that they want to tell the examiner the truth. There should also be
a real fear of failing the test. Your brother questioning you about who
stole the cookie from the cookie jar wouldn't cut it.
As far as I can tell, the goal of the test is to make you spill your
guts. You might consider yourself confident or be a pathological liar,
but when you're afraid of lying, your body will react to it. It's a
very unique experience and I don't think practicing lying or rehearsing
your responses would be useful. They'll dwell on questions that they
think you're trying to deceive them on and ask you over and over. Each
time, you'll give them a little more ("well, one time, but I didn't
inhale!") to get them off your back. They'll do the good cop/bad cop
routine and occasionally storm out of the room. Eventually, hours later,
you'll crack and think, "fuck it, I've already told them this much, might
as well give them the rest." At that point, you're probably crying or
look pretty distraught so they know they've got
everything.
A mock interrogation would not be very effective. The most important aspect of a polygraph is leverage. There has to be an incentive for the person being questioned (e.g. they want an out for committing a crime) so that they want to tell the examiner the truth. There should also be a real fear of failing the test. Your brother questioning you about who stole the cookie from the cookie jar wouldn't cut it.
As far as I can tell, the goal of the test is to make you spill your guts. You might consider yourself confident or be a pathological liar, but when you're afraid of lying, your body will react to it. It's a very unique experience and I don't think practicing lying or rehearsing your responses would be useful. They'll dwell on questions that they think you're trying to deceive them on and ask you over and over. Each time, you'll give them a little more ("well, one time, but I didn't inhale!") to get them off your back. They'll do the good cop/bad cop routine and occasionally storm out of the room. Eventually, hours later, you'll crack and think, "fuck it, I've already told them this much, might as well give them the rest." At that point, you're probably crying or look pretty distraught so they know they've got everything.