this is Mama talking ; this is Mama's talking

Question

Dear Papa will not salute the Stars and Stripes. “An Edgefield man would die first,” Papa says. Yet he doesn’t like it when Mama quotes Mark Twain, who has recently written that Old Glory should be changed to a pirate flag, with black stripes and each star a skull and crossbones. As long as this great land of ours is fighting, the men aren’t fussy about who they fight -- this is Mama talking with her small bent smile. Papa smiles, too, but he is wary. Mama’s needles fly as she quotes from an editorial read at the library, “The taste of Empire is in the mouth of the people, even as the taste of blood --‘”
(Killing Mister Watson, by Peter Matthiessen)

‘This’ seems to refer to the anterior sentence, 'As long as this great land of ours is fighting, the men aren’t fussy about who they fight.' And the head of predicative complement, which is ‘Mama talking with her small bent smile’, is ‘talking.’ However, the modifier of ‘talking’ isn’t possessive case, Mama’s. Can we say both ‘this is Mama’s talking’ and ‘this is Mama talking’? Or is there any other reason to say that way?

Answer 1

"This is mamma talking" is a statement about what's happening. Similar to the "it" in "it is raining", the "this" refers to the general situation. The fragment is broadly equivalent to "What you have just seen is mamma talking" (or, hey, even just "Mamma is talking").

"This is mamma's talking" would be a statement specifically about the talking. In this case, it would be rather unnatural, since we normally refer to an "act of talking" as a speech or something like that.

A pair of examples that might help to tease out the difference:

Papa said he made the mistake because something distracted him – that was mamma's talking.

Papa said he made the mistake because somebody distracted him – that was mamma talking.

In the first case, the distraction was talking (and, specifically, it was mamma who was talking). In the second case, the distraction was mamma (and, specifically, she was talking); in this case, you could also legitimately put a comma before "talking".

Answer 2

In this case I think the context demands that we take talking heads as a participle clause modifying Mama—many linguists (e.g. John Lawler) would probably say it is a relative clause reduced by whiz deletion, who is talking. The purpose of the head clause this is Mama talking is clearly to identify the speaker, which might otherwise be ambiguous.

In any case I think we have to rule out talking as a gerund. We use talking that way only to designate the activity, not the content.

Mama's talking while he was trying to read annoyed Papa.

If the content of Mama's speech is intended we have to incorporate it by allusion.

Mama's talking this way annoyed Papa.