When the three arrived at the Astronomy Tower...
The first thing they saw was an oversized copper cauldron, with Gubraithian Fire swaying slightly in the wind beneath it.
Several professors had already arrived. When Professor Sinistra saw the three of them, she hurried over to greet them.
"Minerva, Pomona, and Douglas, welcome."
Then she said quietly to Douglas:
"I must thank you for inviting Albus, too. Without him, we wouldn't have such a lavish spread tonight!"
After saying this, she gave Douglas a cheerful wink.
Walking up to the hot pot, Douglas greeted each of the professors. Besides Dumbledore and the other three professors, there were Bathsheba Babbling, the Ancient Runes professor; Filius Flitwick, the Charms professor; Charity Burbage, the Muggle Studies professor; and Septima Vector, the Arithmancy teacher.
Douglas noticed that there was actually a small four-tiered stand in front of each person's seat, already laden with dishes.
He took out the cola he had prepared.
Professor Charity Burbage, who taught Muggle Studies, recognized the drink from the Muggle world at once:
"Oh, Merlin's beard, it's cola.
"This is a Muggle drink. Like champagne, it's a sparkling beverage.
"But it has a licorice flavor that you won't find in any kind of champagne, and it contains no alcohol.
"I never expected Professor Holmes to bring it into the wizarding world."
Professor Burbage had not taught at the school when Douglas was a student, so he was less familiar with her than with the other professors.
Douglas handed out the cola to the professors, then said:
"Professor Burbage is right. Most importantly, cola is sweet..."
No sooner had he spoken than Dumbledore let out an "Oh!"
Then the bottle cap vanished, and Dumbledore poured an entire bottle of cola straight into his mouth.
Then he let out a long burp.