A: Jake broke up with his girlfriend because he found that she wasn’t honest with him about her age.

B: I’m not surprised at all. When she said she was 20, I knew she was lying through her teeth!

A: But can you believe that she is almost 45?

B: Wow! She does look much younger than her age.

Note: This idiom means to “lie grossly or maliciously.” People also say “lying in one’s throat/teeth.” Think of this: When people are trying to tell a blatant lie, but fail miserably to cover it up, they say it through clenched teeth (because they are nervous).