Two oyster-related Katrina relief events are happening this weekend. Oyster-Shucking Demonstration at the Grand Army Plaza Greenmarket (Brooklyn): The owner/chef of The Minnow, a seafood restaurant in Park Slope, will be demonstrating oyster-shucking at the Greenmarket on Saturday between 10 a.m - 12 p.m. Hi miniature po'boys will sell for a suggested donation of $2. All proceeds go to UNICEF’s relief work in the areas affected by Katrina. Oyster Festival at Grand Central Oyster Bar (Manhattan): This Friday and Saturday, the Oyster Bar is holding an oyster festival. On Saturday at 1 p.m., Michael Broadway, an oyster shucker from New Orleans, will be opening oysters at an impressive rate. You can pledge money to Katrina-related charities for each one he opens in a minute. There will also be cooking demonstrations and an oyster-eating contest.