The film is set in the medieval period, with Max von Sydow's character being a knight who has returned from fighting holy wars. His chess opponent is Death (to whom he obviously has not yet lost, but continues to play).

Regardless of whether his man-servant appreciated being rudely awakened, he would do well to hold his tongue and prepare himself to fulfil his master's wishes. Mouthing silent profanities behind somebody's back would certainly have been a safer option than speaking up and potentially losing his position or even his life.

From a film-making perspective, it is a clever ploy to emphasise the point by getting him to open his mouth ready to speak, then to quickly change his mind as he considers the scale of the injustice he suffered and the effect his complaining might have. However, I don't know about Bergman's research before making this film, or how much free-rein he allowed his actors.

Follow on question... It looks very animalistic to me, was this an inspiration?

The title is based on the passage: "And when the Lamb had opened the seventh seal, there was silence in heaven about the space of half an hour". The film in general seems to have heavily symbolism towards silence and the silent snarl of discontent from his servant just adds to the symbolism of the film.