He wonders how large the landscape of a given memory may be—whether it is a snapshot of the entire world, or if they cannot actually explore places in a memory that they didn’t know. They decide to explore one to find out, and it appears to be something in between. They are not limited to reenacting exactly what happened in the memory, side-by-side with the memory frames of themselves. They have freedom now to go elsewhere. If they go someplace that didn’t feature in that memory, but that they have other memories of, then it appears the same as any memory. Their memories, it would appear, fuse together cohesively, as they would not have done in a Pensieve.