According to a footnote to this passage (from Rudyard Kipling's "The Mark of the Beast") in The Broadview Anthology of British Literature, vol. V: The Victorian Era, ed. Joseph Black et al. (Broadview Press, 2006), p. 779, note 1:

1 talking “horse” Bragging.
http://www.broadviewpress.com/babl/index.php?option=com_docm...

I do not know for certain that this is right, but it is certainly a respectable scholarly edition of the work edited by well-regarded American specialists.

The first thing that "talking horse" suggested to me (apart from Mr Ed, and of course talking about horses, a sense in which Kipling actually uses the expression elsewhere) was "talking horsesh*t", but I think it's very unlikely that Kipling meant that; it just doesn't sound like a Victorian British expression.

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Note added at 6 hrs (2011-07-21 06:52:58 GMT)
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Curiously enough, I've just found this in an English-Romanian dictionary entry:

"to brag [bragged|bragged] {vb} (also: to butter up, to give lip-service to, to flatter, to talk horse)"
http://en.bab.la/dictionary/english-romanian/brag

I say curiously, because "brag" and "butter up/flatter" are quite different in meaning. However, this does seem somehow relevant to the question of how "talk horse" came to be translated "engatusar" in the version cited by Taña.

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Note added at 6 hrs (2011-07-21 06:56:19 GMT)
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Also this: "to talk horse= to talk big or boastfully, brag"
http://www.usingenglish.com/forum/ask-teacher/131871-talking...

And a few more such entries here and there. There does seem to be something in it.