Foolish
If you give Splinter your heart you'll feel pretty foolish afterwards. His heart belongs to the art of ninjutsu!
You were foolish to give your heart away to Splinter. He didn't want it. Also he's a rat, what's wrong with you?
ぐ
おろ
None
Splinter tells you to your face how foolish you are and you feel your heart turn to goo (ぐ). Now you can't even give it to someone else. No one wants goo.
What will you do with your foolish goo heart now?