In "The Oracle of the Dog" by G. K. Chesterton, Father Brown was talking about someone, saying:
"To be found with a weapon, let alone a blood-stained weapon, would be fatal in the search that was certain to follow. If he left it anywhere, it would be found and probably traced. Even if he threw it into the sea the action might be noticed, and thought noticeable—unless indeed he could think of some more natural way of covering the action. As you know, he did think of one, and a very good one. Being the only one of you with a watch, he told you it was not yet time to return, strolled a little farther, and started the game of throwing in sticks for the retriever. But how his eyes must have rolled darkly over all that desolate sea-shore before they alighted on the dog!”
What's meant here by "thought noticeable", as he already said that "the action might be noticed"?
And does "how his eyes ..." mean "it's a big wonder that his eyes ..."? If so, does Father Brown mean that this happened before this person started the game of throwing in sticks, and then he got the idea?