As the slain Goliath falls, the soles of his shoes bear a twentieth century, rubber waffle tread.
The Philistines are called Barbarians. The word "Barbarian" came into existence during the era of the Roman Empire, 27 BC to 476 AD.
After David beans Goliath, he decapitates the giant with the giant's own sword (bloodless, by the way) and throws the sword down by Goliath's severed head. Camera cuts to a shot of Saul, happy. In the next shot, Goliath's sword is suddenly back in David's hands, held aloft and threatening the Armor-Bearer with it.
Subtitles (when engaged) call out "rain and thunder," but at no point in the film does it ever rain.
Fourteen or so character names appear in the cast list that never come up in the movie; however, one soldier is called Jabeth by name - a speaking role that does not appear in the credits by that name.
Saul's soldiers stand swordless as they watch David and Goliath fight. After David's win, they cheer a lot then storm after the Philistines with swords in hand, pulled out from nowhere.
Inexpert CGI effects in creating images for a multitude of Philistines ends up showing the presence of many more giants than just Goliath.