[bobfunk]

Well, it's worth noting that while we're interested in the general science of puppies and conversions, our end goal with this test was not to determine the exact value of the puppy picture, but just generally finding the best way to get people to click our call to action button...

[LargeWu]

Except you have 2 variables - puppy/no puppy; and copy A/copy B, and therefore 4 combinations. You only tested two combinations, so you have no way of knowing if the puppy or the alternate copy was the reason for the increase.

[herbig]

But how do you determine the best way by introducing multiple variables into your experiment?

The best way may be with the puppy or without. From this you have no idea.