Due to the temporary paralysis, there was little Zabuza could do other than sit and think. One subject his thoughts drifted to was his young cousin from Konoha and from there to the rest of his family. He had no doubt that the kid Naruto was related, he yelled just like his mother did after his father had come home drunk and he'd charged at a much stronger opponent with little regard for his safety the way his uncles and younger cousins had been wont to do. The kid ran the same way they did too.
His mother had been the eldest of seven children. When Whirlpool was decimated by the forces of Lightening, there had been an argument about where the family would go. His mother Karin, the twins Ryu and Kenji and the second youngest sister, Momoko wanted to go to Mist. The eldest son, Sato had wanted to go to Konoha as did his youngest brother Ao and the youngest of the girls, Kushina.
In the end they went their separate ways. Momoko got sick on the voyage over and died less than a week after they arrived in Mist. His mother had died prematurely giving birth to his little sister who had been stillborn. The deaths of his uncles and his cousins who fortunately had been a year or two behind him had been one of his reasons for wanting to kill the Mizukage.
He had thought that he had no family left, but thanks to the Uzumaki refusal to back down no matter what, that wasn't the case.