Table: episode_data_51
Columns: no_in_series
no_in_season
title
directed_by
written_by
original_air_date
production_code

Question: How many episodes were written by Gregg Mettler?
SQL: SELECT COUNT("no_in_series") FROM episode_data_51 WHERE "written_by" = 'Gregg Mettler'

Question: What date did episode 4 in the season originally air?
SQL: SELECT "original_air_date" FROM episode_data_51 WHERE "no_in_season" = 4

Question: What date did "the big giant head returns again (part 1)" originally air?
SQL: SELECT "original_air_date" FROM episode_data_51 WHERE "title" = '"The Big Giant Head Returns Again (Part 1)"'