Revealing mistake: In the first scene when Bridget makes her way up her parent's driveway, you can see her shadow against the cobbled post. However, the sun isn't out and it's cloudy, cold weather overhead. (00:01:15)
Revealing mistake: When they're driving back to the Darcys' in the snow, you can see that as they pass through the village near the house, the snow on the ground is in fact a white ground sheet and has not been pulled up to the edges of the wall surrounding the green. (01:17:25)
Answer: The knickers are almost like spanx or the ones that try to hold everything in and appear skinny. Never particularly sexy! I think that's the joke is she wasn't in anything lacy as she didn't think anyone would be seeing them.