The grammatical yoga teacher

My sister  Anne  instructs  aspiring yoga teachers and she told me that one of her students corrected her grammar.     The student advised  her not to tell the class to "lay down" because lay is only used for things and lie is  used for people.    I told my sister to inform her student that the technical reason to select lie when telling the class to lie on their mats is that  lie is an intransitive verb and lay is a transitive verb.  Transitive verbs always need a direct object.   Intransitive verbs do not. .