Tolkien probably would have been very interested in the debate, as it concerns the use of an Anglo-Saxon word "hwaet" for which we have no exact translation. I thought that Heaney's use of "So." made sense in conveying the down-to-earth voice of the Beowulf poet, better than the "Hark!" or "Listen!" of previous translations.
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I wonder what Tolkien would have had to say about this!