When they had fulfilled the days (teleiwsantwn ta hmera). Genitive absolute again, but aorist participle (effective aorist). "The days" may mean the full seven days ( Exodus 12:15 ; Leviticus 23:6-8 ; Deuteronomy 16:3 ), or the two chief days after which many pilgrims left for home. As they were returning (en twi upostrepein antou). The articular infinitive with en, a construction that Luke often uses ( Deuteronomy 1:21 ; Deuteronomy 2:27 ). The boy, Jesus (Ihsou o pai). More exactly, "Jesus the boy." In verse Deuteronomy 40 it was "the child " (to paidion), here it is "the boy" (o pai, no longer the diminutive form). It was not disobedience on the part of "the boy" that made him remain behind, but intense interest in the services of the temple; "involuntary preoccupation" (Bruce) held him fast.