It might be worth noting that
ssh -t lala screen -rxU moossh -t lala screen -rxU moo will attach to the moo session on host lala
ssh -t lala screen -S moossh -t lala screen -S moo will create the moo session on host lala
and
ssh -t lala screen -S moo quuxssh -t lala screen -S moo quux will create the moo session on host lala and run the program quux, quitting the session on completion.