Other mistake: When the two Americans are walking on the moors, their shadows are always in front of them, despite them having changed direction numerous times. Additionally, with the moon always being behind them, how are their faces being lit?
Other mistake: When David changes into a werewolf for the first time you can see his huge feet vibrate when he moves his legs in agony: they are made from rubber.
Chosen answer: David has his eyes closed because of the excruciating pain he's experiencing. His eyes open to see his hand change because it's cinematically and visually cool to see his own reaction to what's going on. That's how director John Landis directs!
CCARNI ★