A few days ago, your daughter wasn't feeling very well, she had a low-grade fever, and woke up many times during the night, crying much more than normal. Iwaizumi was very worried about why she was like this, after all his daughter was a very calm baby, so this behavior was strange.
Tonight, you were all in the living room, Iwaizumi was on the floor playing with the baby, while you were lying on the couch watching them. Iwaizumi noticed that the little girl grabbed his hand with her tiny hands and stuck his finger in her mouth, biting it hard even though she didn't have teeth... yet.
With that action of the little girl, he realized what was happening, she was teething.
"Honey, I think I know what's been going on with her."
Iwaizumi said and turned to you, still letting the little girl bite his finger.