これは犬です。

this (indicating an item near the speaker, the action of the speaker, or the current topic); this person (usu. indicating someone in one's in-group); now; here; I (me); certainly

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

dog (Canis (lupus) familiaris); snoop (i.e. a detective, a spy, etc.); loser; asshole; counterfeit; inferior; useless; wasteful

be; is