Around the time that Shakespeare wrote Romeo and Juliet, he wrote a comedy called A Midsummer Night’s Dream that has common points with our play. One of the characters, a supernatural “fairy” called Puck often interacts with human without the humans knowing it. At one point, Puck says...

Puck:
I am that merry wanderer of the night.
I jest...and make him smile
When I a fat and beam-fed horse beguile,
Neighing in likeness of a filly foal:
And sometime lurk in a gossip's bowl,
In very likeness of a roasted crab;
And when she drinks, against her lips I bob
And on her wither'd dewlap pour the ale.
The wisest aunt, telling the saddest tale,
Sometime for three-foot stool mistaketh, me;
Then slip I from her bum, down topples she,
And 'tailor' cries, and falls into a cough;
And then the whole quire hold their hips and laugh,
And waxen in their mirth, and neeze, and swear
A merrier hour was never wasted there.

At another part of the play, the same Puck talks about how the humans will react to the supernatural behaviors in the play. Oberon, King of the Fairies, talks to Puck:

When they next wake, all this derision
Shall seem a dream and fruitless vision,
...all things shall be peace.

Puck. My fairy lord, this must be done with haste,
For night's swift dragons cut the clouds full fast,
And yonder shines Aurora's harbinger;
At whose approach, ghosts, wandering here and there,
Troop home to churchyards: damned spirits all,
That in crossways and floods have burial,
Already to their wormy beds are gone;
For fear lest day should look their shames upon,
They wilfully themselves exile from light,
And must for aye consort with black-brow'd night.

Oberon: But we are spirits of another sort:
I with the morning's love have oft made sport,
And, like a forester, the groves may tread,
Even till the eastern gate, all fiery red,
Opening on Neptune with fair blessed beams,
Turns into yellow gold his salt green streams.
But, notwithstanding, haste; make no delay:
We may effect this business yet ere day.
[Exit.

Puck. Up and down, up and down;
I will lead them up and down:
I am fear'd in field and town;
Goblin, lead them up and down.

COMEDY AND TRAGEDY IN SHAKESPEARE OFTEN CO-EXIST--WHAT IS HUMOROUS IN MND MAY NOT BE IN R & J. RULES FOR DRAMATIC COMPOSITION IN SHAKESPEARE'S DAY SAID THAT COMEDY AND TRAGEDY DID NOT MIX--SHAKESPEARE ON THE CONTRARY WAS AHEAD OF HIS TIME AND KNEW THAT THEY DID. PLAYS WRITTEN LATER IN HIS CAREER THAT BLEND THE TWO ARE: HAMLET AND KING LEAR.