Nouns fall into two classes based on animacy: animate and inanimate. Animate nouns are those which denote beings in the animal kingdom; when in doubt about whether a noun is animate or not, consult the Dictionary. (Some cases are not obvious; for example, the words for chess pieces are animate; кџкла 'doll' can be either animate or inanimate; and of the several words for a 'dead body,' one is animate, мертвљц.)
The grammatical category of animacy is important because the Accusative case form of certain nouns depends on whether the noun is animate or inanimate.
The Accusative Singular of a #-declension noun is identical to the Genitive if the noun is animate and identical to the Nominative if the noun is inanimate.
The same rule applies to Plural nouns of all declensions:
The Accusative Plural of inanimates is identical to the Nominative, and the Accusative Plural of animates is identical to Genitive Plural.
Animate Inanimate  
Ї знђю ітого профљссора. Ї знђю ітот ресторђн. (#-decl. Sg.)
Ї знђю ітих профессорћв. Ї знђю іти ресторђны. (#-decl. Plur.)
  Ї знђю іти словђ. (o-decl. Plur.)
Ї знђю ітих жљнщин. Ї знђю іти пьљсы. (a-decl. Plur.)
Ї знђю ітих мышљй. Ї знђю іти двљри. (ь-decl. Plur.)