It might be worth noting that

*ssh -t lala screen -rxU moo* will attach to the **moo** session on host **lala**

*ssh -t lala screen -S moo* will create the **moo** session on host **lala**

and

*ssh -t lala screen -S moo quux* will create the **moo** session on host **lala** and run the program **quux**, quitting the session on completion.