Dr. McDonagh is named after Martin McDonagh. Writer/director André Mileti was working as a set PA on Three Billboards Outside Ebbing, Missouri (2017) simultaneously while filming The Mark (2017) on weekends. Similarly, the lab rats are credited as "Nicolas" and "Victor," a reference to filmmaker Nicolas Winding Refn and executive producer Victor Ho. Mileti worked with the two on The Neon Demon (2016).
Most of the film's budget was raised via Kickstarter. The money raised by the crowdfunding campaign totaled $3,300.