How to keep fit " a romp in the park with the dog " is Miss Heather Thatcher 's method . Miss Heather Thatcher , the actress , finds that the most effective means of keeping fit is to take a daily run in the park with her pet dog Peter . Peter enjoys the fresh air as much as Miss Thatcher and he has learned a number of games . He shows great intelligence during the play . Peter jumps at a signal from his mistress Miss Heather Thatcher , during a run in Hyde Park , London . 10 February 1933