usage - Shakespeare Use of present tense narrating a past action

in Macbeth, Acte III -scene 6,

In this portion of the scene:
« 
Lennox- Sent he to Macduff?

Lord - He did, and with an absolute 'Sir, not I,'
The cloudy messenger turns me his back,

And hums, as who should say 'You'll rue the time
That clogs me with this answer.' »

Why does Shakespeare use present tenses : « turns » and « hums » to narrate a past event ?

Thanks by advance,

Julien