He broke off in mid-sentence, smashed down his fist and surged to his feet when he realized how Adzel and he would be able to rescue Chee Lan from her Merseian kidnappers. See here.
He fell silent and grew tense because of the realization that would lead to the discovery of Mirkheim. See again the second link above.
Here is another. When the Serendipity computer spells out the implications of Satan:
"The idea hit Falkayn in the belly, then soared to his head like champagne bubbles. The money involved wasn't what brought him to his feet shouting. Money was always pleasant to have; but he could get enough for his needs and greeds with less effort. Sheer instinct roused him. He was abruptly a Pleistocene hunter again, on the track of a mammoth.
"'Judas!' he yelled. 'Yes!'" (David Falkayn: Star Trader, p. 358)
Manse Everard bagged a mammoth in the Pleistocene.
There are three indications that the Serendipity partners will now break their own rules and try to acquire Satan:
the computer pauses - Falkayn wonders why but does not suspect anything;
then it strongly advises him, for reasons that cannot be given, not to divulge the truth to anyone else and to spend more time exploring the matter here and now;
when he emerges two hours later, Thea Beldaniel attempts to befriend him and to suggest cooperation.
Serendipity is abandoning its neutrality because, like the computer and Falkayn, it sees a source of great wealth on Satan.