If the author is looking for ideas here, with minimal impact on the existing design, I'd recommend putting the most-recently dropped animal in the back to allow

If the author is looking for ideas here, with minimal impact on the existing design, I'd recommend putting the most-recently dropped animal in the back to allow for cycling through which one you pick up. Another possibility is a "hover" state when when you mouseover a node with 2 animals, they animate quickly into a side-by-side orientation so you can easily pick which one you want to interact with.