Genesis 7:15

And they went in unto Noah into the ark
Noah went in first, and the creatures of themselves came to him, or were conducted by the ministry of angels; and they were delivered into his hands, and he placed them in the ark as was most convenient for them: it is very likely he went in and out as occasion required, for the better management and disposition of things; for he seems to be the last of all that went in, see ( Genesis 7:16 ) : two and two of all flesh, wherein is the breath of life;
they that went by sevens, yet being seven couples, as has been observed, as those which were only two or four, went by pairs: this is true of them all.