Presumably 'hundr', nominative, is the subject of the clause: "and a
dog went with [him]". It's not unsusual for the complement of a
preposition to be omitted like this, e.g. 'ok leggja eigi hug á' "and
pay no attention to it" (Faarlund: The Syntax of Old Norse 7.3).
Which 'þáttr' is it, by the way?

--- In norse_course@yahoogroups.com, "naddr_risi" <emironen@...> wrote:
>
> Here is an excerpt (normalized) from some "þætti":
>
> Sáu þeir þá hvar maðr gekk með vatninu, mikill ok þrýstinn, rak hann
> saman fé ok fór með hundr. Leizt þeim maðrinn ógurligr ok skaut þegar
> skelk í bringu.
>
> The problem is with the expression "ok fór með hundr". You might have
> guessed there should be Dative, "hundi", but all 3 available MSS have
> -r beyond any reasonable doubt. Even 2 of them, distinguishing the so
> called "r rotunda" imply -ur (as you may expect in modern writing).
> Any propositions ?
>