Never fall in love.

This will do the trick. You'll have a good heart with this clock. I have something important to tell you. To be sure you don't turn back into a giant ice-cube forever there are three rules you must always obey. Firstly never touch the hands of your heart. Rule number two: Keep your temper under control. Last but not least, the most important rule: Whatever else you do, never fall in love.

Jack and the Cuckoo-Clock Heart (2013), Mathias Malzieu.