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 ?