Well they use a trick to make sure they aren't switched, which isn't what happens anyhow but...
So the trick is to say; give me a YES, you then should see your finger respond in a YES mode while the opposite; give me a NO should do the opposite.
This was used to determine if they where switched but it really wasn't what was going on.
Better is to say; is 3x3=9, this should give you a positive result same as "give me a YES" since neither one of these critters had math lessons they can't fake this.
Of course occasionaly they get lucky with 2:1 odds...but a second time lets say 4*4=15 can be used to make sure.
If the math to finger results are off you are not in control...