Unfortunately, whenever I think about this or describe it someone, my brain insists on really bad jokes. My apologies to Barry Marshall, since there's nothing funny about his work. But ...
"It really took guts"
"He had intestinal fortitude"
"He had the stomach for the work"
"He swallowed the hypothesis, hook, line, and sinker"
"He put his whole self into his work" (or did he put his whole work into himself?)
"He felt in his gut that he must be right"
"He knew those weren't butterflies in his stomach"
Subject: Silly items