Welcome Darklight
Why not say something like you read in their literature somewhere that there have been more earthquakes since 1914 than in all of history before that. Then say that you decided to check this out on the US Geographical Society website and it says that this isn't true (you can show them the webpage where it says the average has been pretty much the same every year on record). They might then frantically check the Reasoning Book p236. (That, from JW Facts, was a big "seed" for me).
There are plenty of other subtle seeds you can plant. For example they will believe that JWs spoke out against Hitler's tyranny from the word go unlike those evil catholics . You won't need to look too hard through the literature for this kind of claim. You could say that on checking this out you found on wikipedia references to the 1934 Yearbook "declaration of Facts" and Rutherford's letter to Hitler (look up rutherford/hitler). You could say you're confused and wonder what their take on it is. You could say that it doesn't appear to be very politically neutral (references to US and UK as evil wild beast etc, while in support of Germany) (this was another biggie that got me thinking).
Whatever they answer don't react as if you don't believe them, just remain puzzled and say "I'm sure there must be some explanation". Believe me they will go back to others and ask about this because they won't know what to say.
Obviously this depends on whether you can be bothered hehe