Place it right after the moment someone changes their mind, then follow it with Oh My God Wow to underline the reversal. Open the sequence with No No Wait Wait when you want the hesitation to build before the question lands.
關於此聲音
This is a short spoken reaction in Brazilian Portuguese, lasting about two seconds, built around the question of why someone backed out. The delivery sounds puzzled and lightly mocking, like catching a friend changing their mind mid-plan. It works as a quick, pointed response when a promise quietly disappears.