Summary:
According to רש"י, the meaning of ניעו is מי האף (or ליחת החוטם) and according to תוספות it is saliva which is ejected from the mouth through movement.
Summary:
According to רבא; the הללמ"מ teaches us to be lenient by צרורות more than by רגל (to pay a ח"נ [and perhaps even מגופו]). It certainly retains however, the קולות of רגל (i.e. לפוטרו ברה"ר).
לא ראי הקרן שאין הנאה להזיקו - The nature of קרן
which has no pleasure in its damage, is not similar, etc.
Summary:
The גמרא maintained (in this הו"א) that the more difficult it is to contain an animal the less liable the owner should be (for it should be considered כעין אונס). Therefore the characteristics of כוונתו להזיק and יש הנאה להזיקה are reasons to exempt to the owner from payment.