While not the most original format for radio, the Human Zoo was wildly successful. This has been attributed to the particular style of its presenter, who encouraged a very wide variety of callers to contribute, including some who called in to give short performances, play pieces of prepared audio or just shout out catchphrases. "Can I pleasure your wife?" was an oft-repeated slogan. Therefore, the mainstay of the programme for its listeners was the unpredictable nature of where the discussion would lead next. Very weighty issues not often discussed by mainstream phone in radio (which Boyd derided as all about "points missed in the debate so far") could be juxtaposed with frivolous, light-hearted or comedic items. Boyd divided opinion between devoted fans, many of whom considered him to be an extremely wise man, and critics who viewed him as arrogant or mad, often taking the opportunity to phone up to launch personal attacks or deride his ideas with the aim of starting heated and vitriolic arguments.