What present event triggers the flashback in dog star?

In "Dog Star" by Arthur D. H. W. C. R. W. H. W., the present event that triggers the protagonist's flashback is the sight of a dog in the sky, which reminds him of his experiences and memories associated with his time as a soldier. This moment serves as a catalyst for his reflections on his past, particularly his relationship with his dog and the emotional connections he formed during the war. The juxtaposition of the present and the past highlights themes of memory, loss, and the enduring bond between humans and animals.