The mysterious creature first showed up in the Irving residence sometime in 1931, and, according to the accounts of James, Margaret, and Voirrey, initially lived in the walls and, not yet able to speak, imitated a range of animal noises. Quickly, the unseen entity started to pick up human language from the Irvings, and, before long,introduced itself to the family: His name, he said, was “Gef” (pronounced “Jeff”), and he was a mongoose from India.You can read one account of the story here. Not surprisingly, some people - among them the famous ghost-hunter Harry Price - concluded that the Irvings were deluded or hoaxers. Journalists, of course, don't tend to worry too much about the truth in such situations, and Gef made good copy. Things got very silly when Rex Lambert, who co-authored a book about the case with Price, sued a retired colonel for slander because the latter had suggested Lambert must be bonkers for bothering with such nonsense.
One point I find fascinating is this. Nigel Kneale, author of Quatermass and The Stone Tape, was from the Isle of Man. He was born in England, true, but spent much of his boyhood on his ancestral isle. He was born in 1922, and the Gef case was making headlines about ten years later. It's reasonable to conclude that young Nigel must have had his imagination stimulated by a weird haunting involving a talking animal. Is it surprising that he went on to write tales of the paranormal, among them an entire series featuring various weird Beasts? Especially since, in the first and most disturbing episode, 'Baby', the plot revolves around a mysterious animal that is found inside the walls of a country cottage.