According to : http://search.cpan.org/~rgiersig/Expect-1.21/Expect.pod#Is_it_possible_to_use_threads_with_Expect?

Is it possible to use threads with Expect? Basically yes, with one restriction: you must spawn() your programs in the main thread and then pass the Expect objects to the handling threads.

If I don't do this, or call create an Expect object in the main thread, the remote session is 'blocked', unless I pass the expect object to the thread subroutine...