The title is no metaphor - this is literally the story of a boy whose heart is replaced with a cuckoo clock. He is a fragile boy, and is told he may never fall in love, as the stress on his frail, clockwork ticker could kill him.
The movie is based on a concept album by the French band Dionysos - yes, a French band named after the god of wine; who'd have imagined such a thing? - who often feature heavy Roald Dahl and Tim Burton influences. And while I can see a little James and the Giant Peach in there, this stylization has its own very definite look somewhere between cute and creepy.
French pop music is notorious for being terrible, but I quite like the song in the first clip revealed from the movie. I don't understand much of it, but I'm not sure I need to; ignoring the actual words lets me keep an eye out for all the little details, like the fountain that flows backwards. My heart may not be clockwork, but this winds up my nerd senses in all the right ways.
via It's Art