за его мыслью было трудно следить,

за его мыслью было трудно следить, он перескакивал с предмета на предмет

Результаты (английский) 1:

for his thought was hard to follow, he pereskakival with the subject for

Результаты (английский) 2:

for his thought was difficult to follow, he jumped from subject to subject

Результаты (английский) 3:

for him, it was hard to follow, he jumped from the object to the object