After 86ing his wife's friend, the cast was solidified, except for the noise-hating creatures. Since opening a portal to a real monster dimension was apparently too much trouble for the production, they merely employed some good ol' CGI. On set, the usual bored-looking dudes in checkered motion capture suits terrorized the Abbott family:
What you might not know is that for some scenes, Krasinski himself donned the mocap suit to play an alien ... which didn't go over well in early test screenings. Or went too well, depending on how you look at it. With unfinished visual effects, instead of Giger-esque beasts, audiences were somehow expected to recoil in terror at the sight of Jim from The Office bouncing around in a leotard. Not surprisingly, people "burst out laughing." Sadly, that footage hasn't surfaced online, likely incinerated by the producers of Jack Ryan.