A Number? The Number? Has or Have?

Subject/verb agreement can be frustrating, but not getting it right can muddle your writing. In a recent USA Today article about agribusiness, a California poultry veterinarian was quoted as saying this:

It (giving hens more room to move around) has a number of consequences that has potential to be hazardous to bird health and human health.

The basic rule with "number" is that "a number of" is considered plural, as in "A number of my friends have noticed my new car."

However, "the number of" is considered singular, as in "The number of people with new cars is dwindling."

The sentence about the hens should read as follows:

It has a number of consequences that have the potential to be hazardous to bird health and to human health. (In other words, SEVERAL consequences (plural) may result.)