Sentence examples for her knickers from inspiring English sources

Her knickers — her thong.

Her knickers came after his ear.

"Showing her knickers, anything, it didn't matter.

She whips a pistol from her knickers".

Did she really flash her knickers at David Trimble?

Tracey Emin throws her knickers on to the bed.

And you can't even quite see her knickers.

"She has to change her knickers every hour.

You can't say anything these days, can you, without some feminist getting her knickers in a twist?

As the phenomenon grew more pronounced, she touched the area tentatively, over the cotton of her knickers.

Anyway, my question is, what's does the line "sows a bird in her knickers" mean?