Conversation so far:
when did they start adding candles to birthday cakes
Though the exact origin and significance of the candle blowing ritual is unknown, there are multiple theories which try to explain this tradition.
what is one theory for the birthday candle ritual
One theory is attributed to the early Greeks, who used candles to honor the goddess Artemis' birth on the sixth day of every lunar month.
can you tell me one more theory for the origin of the birthday candle ritual
The use of fire in certain rites dates back to the creation of altars. Birthday candles are said to hold symbolic power.

Question: what is the next one
Self-contained rewrite: what is the next theory for the origin of the birthday candle ritual