I've been reading a text from the book 1100 words you need to know.
Week 6 Day 1. The text is about an invention - an umbrella substitute. In this text, there is a passage where the word "open" is used but I don't understand its meaning. Is it a noun? Is it a verb? Or is it an idiom?
When a person is caught in a sudden rainstorm, he swings the plastic strip open in a shape of a cross
The person already "swings" and what "open" is doing here?
Online source (The original book says the same)