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Warning! This post contains SPOILERS for Marvel's Secret Invasion.
The Marvel's Secret Invasion series sheds light on the challenges of identifying Skrulls in the MCU. However, an easy solution was uncovered seven years ago in Doctor Strange. Unlike the original comics, which featured gadgets to detect Skrulls regardless of their appearance, it has proven difficult to distinguish between shape-shifting aliens and humans in the MCU. Nonetheless, it appears that Nick Fury (played by Samuel L. Jackson) simply requires the assistance of a skilled Master of the Mystic Arts.
Marvel's Secret Invasion is an incredibly suspenseful show, brimming with paranoia. Up until now, the primary methods of identifying Skrulls involved encountering their true form upon death or resorting to brutal interrogation and torture, exemplified by Sonya Falsworth (portrayed by Olivia Colman) severing a Skrull's finger. However, the MCU has a diverse array of characters who possess the innate ability to expose any disguise and perceive the true identity of individuals, such as a Skrull impostor.
MCU Wizards Can Easily Identify Skrulls
In the MCU, sorcerers such as Doctor Strange, Wong, and their fellow magic users from Kamar-Taj possess the ability to detach an individual's astral form from their physical body. The initial demonstration of this power occurred when Stephen Strange experienced it firsthand upon encountering the Ancient One in the 2016 film Doctor Strange. Subsequently, we witnessed the Hulk, portrayed by Bruce Banner, undergo the same phenomenon in Avengers: Infinity War, and Peter Parker in Spider-Man: No Way Home. Consequently, it is highly probable that separating an individual's astral form would immediately expose whether they are a Skrull impostor or not.
Why Fury Hasn't Contacted Doctor Strange
Soul-checking every individual on Earth is clearly impractical. This is especially true considering that Talos mentioned in Secret Invasion episode 2 that a million Skrulls are now living in secrecy among humanity. However, it would be relatively easy to conduct soul-checks on the Avengers, influential global leaders, and other prominent figures worldwide. Implementing such measures would effectively protect the world from the most dangerous Skrull impostors, similar to the unexpected Rhodey/Skrull twist in Secret Invasion.
Before the events of Secret Invasion, Fury was always distrustful, making it difficult for him to trust anyone. In addition, it is unlikely that Fury knows Doctor Strange or any of the other wizards from Kamar-Taj in the MCU, as Strange did not join forces with the Avengers until Infinity War. It is also possible that Strange and Wong may not be available during the events of Marvel's Secret Invasion. In the last known sighting, Strange was on his way to the MCU's Dark Dimension, while Wong keeps his location hidden by teleporting as needed. Nevertheless, separating the astral form seems like an ideal method to identify Skrulls in the MCU.