This passage uses personification. Words cannot actually be stiff or heavy, and they do not need to be pushed out of one's mouth, but these adjectives and actions give the reader a vivid picture of Molly trying to say this words, and struggling greatly to do so.
I think you should insert a comma between causes and an
Hi sorry I can not help u but I hope you have a good day.
Answer:
to escape slavery to become free
Explanation: