Stan Winston, responsible for creature effects in "Aliens", was approached but was not available. Winston instead recommended Tom Woodruff Jr. and Alec Gillis, two former workers of his studio who had just started their own company, Amalgamated Dynamics. Even before principal photography had begun, the practical effects crew was developing models of the Alien and the corpses of the "Sulaco" victims. Richard Edlund's Boss Film Studios was hired for compositing and other post-production effects. A small number of shots contain computer-generated imagery, most notably the cracking alien head once the sprinklers cause thermal shock. Other CGI elements include shadows cast by the rod puppet alien, and airborne debris in outdoor scenes.