Warning: MAJOR SPOILERS ahead for Zero Day!Zero Day co-creator Eric Newman has addressed why Robert De Niro’s George Mullen was experiencing hallucinations, unpacking the possible explanations. Throughout the show, Mullen experiences a variety of unrealistic hallucinations, making him think someone is purposefully messing with his mind throughout the show. However, lab results render this idea inconclusive, with the series never directly determining what is causing his hallucinations. Neither Mullen nor any other character in Zero Dayget an explanation, only hints that Proteus may have been used on the former President to mess with his mind.