a soft giggle
A soft giggle is when you laugh but it’s like you’re holding back. It’s like a laugh that’s too shy to be loud.
He did a soft giggle when I told him I could time travel. He was too surprised to laugh loudly.
She did a soft giggle when I told her I had a pet alien. She was confused.
I did a soft giggle when I saw my dog wearing a crown. It was too silly to ignore.