As children we learn (and may also be taught) that singular nouns take singular verbs and plural nouns take plural verbs. This subject–verb agreement is also called concord; it sounds perfectly straightforward, but it often isn’t. Complications arise and mistakes slip in even when the numbers involved seem obvious.
In unedited writing it’s common to find nouns or noun phrases disagreeing with the verb, especially when a string of text comes between them and ends in an element with a different number. Though less common in edited prose, because it’s something editors look out for, examples do occur. Here’s one I read in Chase Novak’s horror novel Breed:
The thick gloomy shadows of the apartment itself, depressing on the face of it, is actually a kind of blessing to Amelie and Bernard, muting the visual impact of Bernard’s countless deformities and hiding, as well, the chaos of their quarters.