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The plot is about a group of people, both men and women, who are exploring a cave underground. They start by sending a black dog down first, but the dog quickly becomes scared and rushes out of the cave. Finding this strange, they decide to venture down themselves. Inside the cave, they encounter many humanoid monsters who are completely bald and hairless. Initially, they only encounter a few of these creatures, but later, millions of them start running towards them.
In the end, they finally find an exit, but it’s located high up. They hold hands and try to reach the opening, but there are too many monsters by then, and they end up being consumed by them. Eventually, it seems like only one girl manages to escape.
Maybe the sequel?:
“The Descent: Part 2” (2009)
This one has a dog in it.
UPDATE (8 March 2024): I downloaded the movie and I have just watched the beginning of the movie and I can confirm that there is a scene early in the movie where they send in a black dog into the cave and a bit later the dog runs out of the cave screaming. This scene with the dog starts ca. 7 minutes and 45 seconds into the movie. So, I am pretty sure that this is the movie you are looking for. Hey, ISIOU, hopefully you read this and you come back and confirm the movie.