Wandering Soul (12:02)
Film Shortage; Films Short; IMDb; Screen Australia; Short of the Week; Vimeo; YouTube

This 2016 short film was presented by Alter in 2022, though I had seen it sometime before that.

Set in 1966, during the Vietnam War, mostly in the Cu Chi Tunnels of South Vietnam. A Vietnamese soldier named Dao buries a fallen comrade, and tries to perform a ritual that I guess would put his soul to rest, so that his ghost wouldn't haunt him. Or something. But a living comrade named Quan interrupts the ritual, wanting to get out of the tunnels before the American soldiers show up. Dao stays behind, but ends up being haunted, despite his efforts. And it is creepy AF, especially with the added claustrophobic conditions that naturally come from being underground. Eventually he and Quan both get to the surface, and... I don't want to spoil the twist that is revealed then, but it's based on actual history, and it's horrifying in its own non-supernatural way.