"or his lamb straying": in the manner of strays. From here it was ruled; What is considered a lost object? If one found an ass or a cow grazing on the road, this is not a lost object. If he found an ox with its load overturned or a cow running in the vineyards, that is a lost object.
"and (you shall) ignore": Sometimes you do ignore (a lost object), and sometimes you do not ignore. How so? If he were a Cohein and the object were in the cemetery, (which a Cohein is forbidden to enter), or if he were an elder (i.e., a Torah scholar) and it were beneath his dignity (to retrieve it), or if his labor (to retrieve it) were greater than that of his neighbor, he is exempt (from retrieving it). This is the intent of "and you ignore" — Sometimes you do ignore and sometimes you do not.