The aliens were played by dancers and stuntmen in lightweight costumes, which allowed them to move quickly. A number of mannequins were used for aliens which were contorted into inhuman poses. Although it appears hordes of alien creatures are in the film, there were only 12 alien suits: simple, black leotards covered in molded foam for faster-moving shots, and detailed models with articulated upper bodies and mouths for closeups. When the aliens were shot and destroyed, puppets were hung up and detonated. The aliens' acidic blood was a combination of tetrachloride, cyclohexylamine, acetic acid, and yellow dye. Winston added arms to the chestburster alien form (since the adult form had arms), explaining how it could drag itself out of a host's chest. Two chestburster puppets were used: a reinforced one, and an articulated one for movement. A puppeteer punched the former through a fabricated latex-foam chest; the scene took several takes to film, because it could not pierce the clothing.