Mum’s, or to use its full title, Mum’s Great Comfort Food, is a restaurant in Edinburgh designed to soothe itinerant performance artists. For, in the fag days of August, as the Fringe dies — it will be reanimated next year by the blood of Citizen Puppet and Nicholas Parsons — assorted actors and comics and cabaret artists and mime artists and circus artists and ballet dancers and tap dancers and flute players and face painters and sketch performers and one-woman-show specialists (expiating rejection by standing in bins) and the guy who dresses up as Darth Vader are more ulcer than...