Looking over one’s shoulder

Looking over one’s shoulder  is an idiom with an uncertain origin. An idiom is a commonly used word, group of words, or phrase that has a figurative meaning that is not easily deduced from its literal definition. Often using descriptive imagery or metaphors, common idioms are words and phrases used in the English language in […]
from Grammarist
https://grammarist.com/idiom/looking-over-ones-shoulder/