An object to treat as the head of an unreachability trace.
+
If no objects are given, git-fsck defaults to using the
-index file and all SHA1 references in .git/refs/* as heads.
+index file, all SHA1 references in .git/refs/*, and all reflogs (unless
+--no-reflogs is given) as heads.
--unreachable::
Print out objects that exist but that aren't readable from any