I remember being little, about 5 or 6 and my parents got me a toy ark with 2 of a lot of animals. After a few days of having it, I noticed several animals were missing (giraffes, dogs, leopards, horses) and came to the conclusion the ark story had to be bullshit.
Then not to mention the one time for a physics class in high school, I did a project just getting the average mass of several animals, adding them to the weight of the ship, and then finding out it would make the ship too dense to float. That rubbed some Christ believers the wrong way.