In cartoons, one often sees the character with a tiny angel on one shoulder and a tiny devil on the other. The angel is the conscience. The devil represents a demon, or perhaps the Freudian Id.
In Pinocchio, the main character is made of wood and lacks a conscience, and is awarded a highly moral, nattily dressed insect named Jimminy Cricket to be his conscience.
One can ignore one's conscience by shaking one's head violently. This makes them fall off one's shoulders and shut the Hell up.
The three visitors to Scrooge, the Spirit of Christmas Past, the Spirit of Christmas Present, and the Spirit of Christmas Future were manifestations that caused Scrooge's conscience to reboot.
The conscience is generally regarded as the moral compass of the individual, that distinguishes right from wrong.
Upon occasion, it seems that the conscience gets ill and informs the individual that Martians are stealing his underwear or are lusting after his spleen, or that weasels are ripping his flesh.