def diff(prev_snapshot, next_snapshot):
    """Return a dict containing changes between two snapshots."""
    changes = {}
    for path in (set(prev_snapshot.keys()) | set(next_snapshot.keys())):
        if path in prev_snapshot and path not in next_snapshot:
            changes[path] = 'Deleted'
        elif path not in prev_snapshot and path in next_snapshot:
            changes[path] = 'Created'
        else:
            prev_mtime = prev_snapshot[path]
            next_mtime = next_snapshot[path]
            if next_mtime > prev_mtime:
                changes[path] = 'Changed'
    return changes
