As for the pronoun, the third person of the male gender is used. as for the noun only "s" is added since the word "reloj" ends in consonant to be plural. For the adjective Spanish differs from English, in this case as for the noun "s" is added.
The reason why Holmes put his ear to the ground was beacuse his boss told him to. Also so he kept his ear to the ground, so that he would be the first to get a new idea.