What is the origin of "to lie through one's teeth"?

I read the origins of this saying are quite old:

"...traceable to the early 1300's as in THE ROMANCES OF SIR GUY OF WARWICK,"

According to this: https://www.englishforums.com/English/EtymologyThroughTeeth/jhphl/post.htm

Did this apparently obscure reference serve as the source of the saying, or was it defined earlier and then used in this text?

Bonus question: Does lying through the teeth imply with a smile?

Solution 1:

According to The Phrase Finder the expression might be a variant of a similar expression which dates back to the 14th century and adds: "the OED mentions lying "in his teeth," but without any further information":

Lie in one's teeth:

• "To accuse a person of lying in his teeth is the strongest of accusations, implying that the person is such a double-dyed liar as to be unfamiliar with truth.

• It is very old traceable to the early 1300s, as in 'The romances of Sir Guy of Warwick,' 'Thou liest amidward and therefore have though maugreth (shown ill will).'"

• (From "Hog on Ice & Other Curious Expressions" (1948, Harper & Row) by Charles Earle Funk.)

The following source:

• cites a usage example of "lie in his teeth" from the "History of New York" (1812) while the first documented usage of 'lie through one's teeth' is from the novel "love me or love me not" by Mrs. Francis G. Faithfull (1875).

(Idioms in the News - 1,000 Phrases)

Ngram: lying through his teeth vs lying in his teeth.

As for your second question, "Poplollies & Bellibones/Tenderfeet & Ladyfingers: A Celebration of Lost Words/A Compendium of Body Language", suggests that lying through one's teeth implies a (deceiving) smile:

• A person known to lie through his teeth has no compunction about telling falsehoods. But why through his teeth? The liar has to force himself to assume the calm demeanor that will conceal his duplicity. He attempts a hearty smile,.....