This is the 5451st most frequent Korean word.
마리를
"마리를" is the accusative form of "머리," meaning "head" or "counter for animals" in Korean.
The word '마리가' indicates the number of rabbits, three ('세'), doing the action in the sentence, used as part of counting animals.
밭에 토끼 세 마리가 뛰어놀고 있어요.
Three rabbits are playing in the field.
In this sentence, '마리를' is used as a classifier for counting animals, specifically indicating the quantity of one ('한') puppy.
나는 강아지 한 마리를 기르고 있어요.
I am raising one puppy.
Here, '마리를' is again a classifier used for counting animals, referring to two ('두') chickens for purchase.