YOU SAID:
I have stabbed my old dog
INTO JAPANESE
老犬を刺してしまった
BACK INTO ENGLISH
I stabbed an old dog
INTO JAPANESE
老犬を刺した
BACK INTO ENGLISH
stabbed an old dog
INTO JAPANESE
老犬を刺した
BACK INTO ENGLISH
stabbed an old dog
That didn't even make that much sense in English.