holy fuck was the alien coming out of that dude improv pic.twitter.com/IZW3K71k3G

— T$E CHUN ➡️ GREMLINS @ SDCC (@thetzechun) July 16, 2022

Not improv in the traditional sense, but the cast did not know what was going to occur or exactly the effect that would be used. They were as shocked as all the viewers were the first time they saw the film. The director wanted to capture their actual reactions so, no, they did not know the chestburster was gonna do some chestburstin’.