Christmas trees were an obscure German tradition, unknown to the English until its introduction by Queen Victoria's husband over 700 years later. Furthermore, even the concept of decorating with glass balls was even unknown to the Germans until long after this era.
Henry refers to the lack of value of Eleanor's signature on paper. Paper was a Chinese invention unknown to Europe at this time. The very first paper mills were not founded in Europe until the 13th Century. Instead, parchment was used at this time.
The song Alais sings while Henry is fighting John is called "Allon, Gay Bergeres." This chanson was written by Guillaume Costeley during the Renaissance, nearly 400 years after the events in the movie take place.
Henry refers to the royal sons in the wine cellar as aging with the royal port. Although acidic Portuguese wines were introduced into England in the 12th Century, port wine was introduced there 500 years later.
Eleanor refers to her first husband as "Simon pure and Simon simple", both of which are anachronisms coming from a late-12th century character. The former refers to a character in the play "A Bold Stroke for a Wife", which would not be written until the early 18th century. The latter refers to the English nursery rhyme "Simple Simon", which cannot be found in any reliable source before the late 17th century.
During a scene in the dining hall, Henry is watching his jesters perform. At one point, he throws his head back with his mouth open as he roars with laughter. Metal fillings are clearly visible in his upper molars.
At one point Henry asks Alais rhetorically "Has my willow become poison oak?" Poison oak is a shrub endemic to western North America and its existence would have been unknown in Britain in the 12th century.
For a moment Eleanor appears in front of Henry and Alais. Then she puts her hands one on the other, about her breast, and says to Henry she wants to watch him to kiss Alais. In the following shot her hands had changed position.
After Henry asks for an annulment from Eleanor, he gets up from his chair, crosses the room, and leans forward against a stone pillar. When Eleanor follows him in the next shot, as she draws closer to him, he is standing in the middle of the room, nowhere near a pillar.
During the fight between Eleanor's guard and the jail-keep, Eleanor's guard pushes the other against the wall and knocks the sword out of his hand. When the jail-keep draws his knife, suddenly Eleanor's guard is against the wall instead.
At one point Eleanor states that the year is 1183. At another point Henry II claims "I'm 50 now! Good God, boy. I'm the oldest man I know. I've got a decade on the Pope!" However, the pope in 1183 was Lucius III who was born in Lucca Italy in 1097. Henry II was born on 5 March 1133, making him 36 years younger than the pope.
At the beginning of the film, Henry compares his situation to that of King Lear. Although Shakespeare wrote King Lear more than 400 years after the death of Henry II, it was based on a legend of Leir of Britain as recounted by Geoffrey of Monmouth, who was alive in Henry II's day.
During the battle at the beginning of the movie, the second group of ambushing mounted warriors charge onto the beach from their hiding place in the rocks. Although it is supposed to be a surprise attack, the pathway from the hiding place to the battle, on otherwise pristine sand, is visible from previous takes.
When Eleanor lights a torch and steps down the stairs followed by a guard, the torch shadow projects on the guard and, after, on the wall on the left. It is supposed to be the only light came from the torch.