Conversation so far:
What activities did the Algonquin Round Table do?
In addition to the daily luncheons, members of the Round Table worked and associated with each other almost constantly.
Did the Algonquin Round Table play a lot of games?
The group was devoted to games, including cribbage and poker.
What else did the Algonquin Round Table do besides cribbage and poker?
The Algonquin Round Table also played charades.
Did members of the Algonquin Round Table work in writing
A number of the members of the Algonquin Round Table had regular newspaper columns
What did the charter members of theAlgonquin Round Table do for work?
Charter members of the Algonquin Round Table included a columnist, playwright, freelance writer, poet, etc.
What else did theAlgonquin Round Table club do besides cribbage, poker, and charades?
A number of Round Tablers were inveterate practical jokers, constantly pulling pranks on one another.
Did the Algonquin Round Table pull any good pranks?
As time went on the jokes became ever more elaborate. Harold Ross and Jane Grant once spent weeks playing a particularly memorable joke.

Question: what was the prank
Self-contained rewrite: What was the prank that Algonquin Round Table Harold Ross and Jane Grant once spent weeks playing?