Background: The Algonquin Round Table was a group of New York City writers, critics, actors, and wits. Gathering initially as part of a practical joke, members of "The Vicious Circle", as they dubbed themselves, met for lunch each day at the Algonquin Hotel from 1919 until roughly 1929. At these luncheons they engaged in wisecracks, wordplay, and witticisms that, through the newspaper columns of Round Table members, were disseminated across the country. Daily association with each other, both at the luncheons and outside of them, inspired members of the Circle to collaborate creatively.
Context: In addition to the daily luncheons, members of the Round Table worked and associated with each other almost constantly. The group was devoted to games, including cribbage and poker. The group had its own poker club, the Thanatopsis Literary and Inside Straight Club, which met at the hotel on Saturday nights. Regulars at the game included Kaufman, Adams, Broun, Ross and Woollcott, with non-Round Tablers Herbert Bayard Swope, silk merchant Paul Hyde Bonner, baking heir Raoul Fleischmann, actor Harpo Marx, and writer Ring Lardner sometimes sitting in. The group also played charades (which they called simply "The Game") and the "I can give you a sentence" game, which spawned Dorothy Parker's memorable sentence using the word horticulture: "You can lead a horticulture but you can't make her think."  Members often visited Neshobe Island, a private island co-owned by several "Algonks"--but governed by Woollcott as a "benevolent tyrant", as his biographer Samuel Hopkins Adams charitably put it--located on several acres in the middle of Lake Bomoseen in Vermont. There they would engage in their usual array of games including Wink murder, which they called simply "Murder", plus croquet.  A number of Round Tablers were inveterate practical jokers, constantly pulling pranks on one another. As time went on the jokes became ever more elaborate. Harold Ross and Jane Grant once spent weeks playing a particularly memorable joke on Woollcott involving a prized portrait of himself. They had several copies made, each slightly more askew than the last, and would periodically secretly swap them out and then later comment to Woollcott "What on earth is wrong with your portrait?" until Woollcott was beside himself. Eventually they returned the original portrait.
Question: What kinds of pranks did they pull?. Whats the answer?
playing a particularly memorable joke on Woollcott involving a prized portrait of himself.