As you sink into the fifth season of the elegant world of Downton Abbey, spare a thought to what it takes to make it seem so true to the 1920s.
You can chalk the authenticity up to Alastair Bruce, the historical adviser, who makes sure that everyone's backbone is straight and there's no handshaking or clicking of glasses.
"The aristocrats that ruled in England, and their servants, lived by a very odd set of rules," explains Bruce in "The Manners of Downton Abbey," which will, in many areas, accompany Sunday's premiere of Season Five on PBS.
"Manners came into everything — how you dressed, how you ate, how you stood and how you spoke. ... They were a secret code that tells you everything about Edwardian England."
Revisiting the period was difficult for a modern cast.
Tom Cullen, who plays Tony Gillingham, a suitor of eldest daughter Lady Mary Grantham (Michelle Dockery), said, "I love Alastair. He's literally taught me everything. How to tie my shoe laces, how to gesture, how to stand."
"The main thing I had to learn was posture, was this idea of sitting up straight," says Lily James, who plays Lady Rose MacClare.
"The back of a chair was never for anyone to lean back on," explains Bruce. "It was purely decorative."
He adds, "Nannies used to put knives here," running his hand up and down the inside of the back of a chair, "to make children sit up straight." (Which may explain why so many dining room chairs had uncomfortably knobby elaborately carved backs).
"Clothes mattered to the Edwardians because every detail meant something," Bruce says. "Ladies' dress was extravagantly elaborate and guided by a myriad rules."
For example, they defined who can wear a tiara, or can't. According to that period's society, only married women were allowed to wear them.
There are many rules "involving gloves. When you have the gloves on, when you have them off," James says.
"Even in the drawing room," says Dockery, "you have to leave your gloves on."
"On a usual day, (the women) dress for breakfast," says Joanne Froggatt (Anna Bates), the lady's maid. "Then they'll change if they go for a walk in the morning or go riding, then change for lunch; and then they may change for the afternoon. If they sit and read or go visit someone, then they'll change again for dinner. Basically these ladies spend most of their time changing."
The rules for gentlemen's wear "remained resolutely stiff," Bruce says. "A statement of control in a shifting world."
The elegant white tie dinner suits were very uncomfortable with excessive starch in the "cardboard kind of shirt," according to Cullen. "They're so horrible."
In the end, it comes down to a question asked during one episode by Tom Branson (Allen Leech), a newcomer to high society. "But, why do the rituals, the clothes, and the customs matter so much?"
It's the Dowager Countess of Grantham (Maggie Smith) who explains very simply: "Because, without them, we'd be like the wild men of Borneo.