Why is it "lay still" instead of "lie still" in this scene in Wonderwoman?

Question

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This is from Wonder Woman, and a woman on the left is laying the wounded woman down on the grass.

She says to the hurt woman, "lay still."

I don't understand why it's "lay still" instead of "lie still".

I already googled the difference between "lie" and "lay" and lay is a transitive verb which needs an object. It also doesn't make sense if lay here was used as a past form of "lie", since in this scene, the woman is ordering(not exactly ordering in the sense of forcing someone) the wounded woman to lie down still and thus present verb should be used.

What am I missing? Why is it "lay"?

Answer 1

Because the movie is wrong; you are correct: "Lie still."

This article from Merriam-Webster supports your correct understanding: (bold emphasis added)

Lay means "to place something down flat," while lie means "to be in a flat position on a surface."

Most native speakers of any language have their common, vernacular errors. Native speakers often get this wrong, including myself. It is a bad habit to be anticipated and it is perfectly fine to correct us when we do, though some on the IPS may say correcting others' speech is not always most tactful. :-)

Nonetheless, this is a common mistake among native speakers, which indeed makes the language more difficult to learn for second-language learners.

Why do we make this mistake?

Most likely, we make this mistake because "lie" is the same word as to be dishonest...

lie 2 (Merriam-Webster):

to make an untrue statement with intent to deceive

...But that is just a guess. Mistakes happen in every culture and the habits of a culture tend to be contagious within that culture. Don't pick up our bad habit yourself.