There are some sadness faces, and when they touch a laughing face they will switch to be happy. Can you make all these faces to say goodbye to sadness?
Left mouse click: remove a face. Ctrl + Left mouse click: make a smile face to jump. Shift + Left mouse click: make a crying face to jump.
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.