Etaient à se promener. — Were walking

" Se promenaient" could be said, but the former expression more forcibly indicates that they were engaged in the very act of walking.

239. Il a la vie dure : je lui en ai fait bien d'autres, allez ! — He is pretty tough : I hâve given him many a worse one, I warrant you !

240. Tue le donc. — The use of the second person singular hère expresses anger and scorn.