With this phrase, Shakespeare makes a relation between the battle of Macdowald and King Duncan’s men, to a pair of struggling swimmers. What he is trying to do is to put the image of battle into the crowds mind. However he used the word ~cling~ to make the audience thing that the characters are miserable and desperate which has an irony to it because the two sides of soldiers are battling against each other .

October 9, 2016 at 4:04 pm
This is a very strong explanation, Elroy. Don’t forget to mention the original quote and to name the act and scene as this will help you when you come back to it in the future.
CW