Product list -> on hover second image


I would like to offer my visitors two views/images of each product in the grid view of my product listing page.

Example: If you hover over an image/product on the product listing page the second image is on top/replaces the first one.

I tried it with

$product->getThumbnailUrl(0) <-- standard first master image
$product->getThumbnailUrl(1) <-- second image

but only the first image is displayed. Maybe someone can help and give me a hint?

Thank you!