Just as you can see through glass, you can see through the extraordinary glass frog.
Many of these frogs have lime-green skin, but some lack any coloration on their underside, making their organs visible to the naked eye. Equally amazing are their spotted backs, which scientists speculate are meant to resemble eggs – so predators going after their offspring get confused.
Your best chance of spotting this tree-dwelling frog is in Costa Rica or Panama. Costa Rica's Tortuguero National Park in particular promises a good chance of seeing one, in all its transparent glory.