Verses 41-42 explain how Jacob made certain that his animals were stronger and healthier than those that belonged to Laban. See the note on trick 3 in verse 37.

Whenever the stronger of the flock were breeding: stronger of the flock refers to the animals that are robust, sturdy, healthy. In some languages these are called “the fat animals.”

Laid the rods in the runnels: see verse 38.

Before the eyes of the flock: that is, so they could see the striped branches.

That they might breed among the rods: see the similar expression in verse 39.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .