According some Italian folk traditions, while the devotee is praying, she or he observes the manner in which the flame of the petition candle burns. In this way, one may read la lingus delle candelle, "the language of the candle."
If a candle burns high or with a steady flame, that is a good sign.
If the flame crackles, it means a guardian spirit--usually the saint being petitioned, but perhaps one's patron saint or one's own guardian angel--is working to ensure the petition is granted.
If the flame self-extinguishes, that is a bad sign. It may mean that the request was not worthy.
There are other signs as well.
Myth's Notes
Candles were once the primary form of illumination. Folklore abounds with interpretations of candle flames. Some American folk beliefs or lychnomancy follow:
If a spark flies off a candle wick, a message is coming.
Spirits are attracted to candles and a candle can be used for divination. If the candle flickers or sputters, the answer to one's question is "no." If the flame burns steadily or leaps up brightly, the answer is probably "yes."
If a candle flickers, though the air is deathly still, a ghost is present.
If a flame burns blue, a powerful spirit or witch is nearby.
It is bad luck to fall asleep in a room with a burning candle.
Extinguish a candle if it smokes. Snuffing it will "halt" any unpleasant influence from some nearby spirit. On the other hand, the candle may be set in a draft or something is wrong with it.
If a candle flame hisses, sizzles, pops, or makes other such noises, it means the spirits of the dead or good angels are trying to give a message.
A lit candle burning inside a carved-out pumpkin on All Hallow's Eve will keep malign spirits at bay.