If you were wondering what the two of them were looking up at and looked up at the sky yourself, you would see this falling from the sky.
Because the label is blank, we can safely assume that this is totally not a carton of milk.
"Pinkie..." Twilight said with a deadpan tone. "Are you telling Rainbow Dash to fly around dropping trash everywhere again?"
"Hey! I don't tell Dashie to drop trash everywhere! I tell her to drop random objects that she doesn't need anymore everywhere!" Pinkie retorted.
"That's pretty much the same thing! Is that what you just told her to do?"
The carton fell onto the ground and bounced around before coming to a stop right before Pinkie's forehooves. She picked it up and shook it a little, noting that there was still some of its contents inside.
"I don't know why, but I really wanna drink this right now." Pinkie opened up the carton and peered inside to see a dark green liquid.
"Really? You see a carton fall out of the sky and your first idea is to drink it without any precaution whatsoever?" Twilight asked.
"Yeah, pretty much." Pinkie took a mug out of her mane and filled it up with the strange liquid before downing it in multiple swigs.
