 McCay continued to produce animated films using cels . By 1921 , he had completed six , though three were likely never shown commercially to audiences and have survived only in fragments : The Centaurs , Flip 's Circus , and Gertie on Tour . In 1921 , he released three films based on Dream of the Rarebit Fiend : Bug Vaudeville , in which insects and other creepy @-@ crawlies perform on stage ; The Pet , in which a creature with a bottomless appetite grows enormously and terrorizes the city in a way reminiscent of King Kong ; and The Flying House , in which a man attaches wings to his house to flee from debt . McCay 's son Robert is credited with the animation on this last film , but Canemaker notes it is highly unlikely that a first @-@ time animator could have produced such an accomplished piece of animation . 
