He must have moved very quietly to have approached so near without attracting the boy's attention, and that, to Frank, whose suspicions had already been thoroughly aroused, was good evidence that the Ranchero was not just what he ought to be.

If he was an honest man, he would not try to slip around without making any noise.
Finding that he was discovered, Pierre removed his sombrero and said, without the least embarrassment: "Is it your pleasure to ride?
If so, I will saddle your horse." "You need not trouble yourself," replied Frank, rather gruffly.

"I shall remain at home." Pierre bowed and walked away.
"Now, that rascal thinks he is sharp," said Frank, gazing after the Ranchero.

"He never offered to saddle my horse before, and he wouldn't have done it then if I hadn't caught him looking in at the window.

I wonder if he thinks I am foolish enough to ride for pleasure at this time of day, with the thermometer standing a hundred degrees in the shade?
That fellow is a scoundrel, and he is up to something.