He stared at it a long time as if lost in a dreadful dream.

Then he observed that Tom's hands were clenched as though he had fallen facing somebody in a fight with fists.

His knuckles, on closer view, appeared somewhat abraded.

Both hands.
The discovery of these slight signs was more appalling to Byrne than the absolute absence of every mark would have been.

So Tom had died striking against something which could be hit, and yet could kill one without leaving a wound--by a breath.
Terror, hot terror, began to play about Byrne's heart like a tongue of flame that touches and withdraws before it turns a thing to ashes.