YOU SAID:
the hippo i sat on was my brother's hippo maybe he'll be mad at me
INTO JAPANESE
私が座ったカバは私の弟のカバだったかもしれない
BACK INTO ENGLISH
The hippo I sat on might be my brother's hippo
INTO JAPANESE
私が座ったカバは私の弟のカバかもしれません
BACK INTO ENGLISH
The hippo I sat on might be my brother's hippo
You've done this before, haven't you.