What are the keywords of the episode "Shield"?
the episode "Shield" refers to title = 'Shield'
SELECT T2.keyword FROM Episode AS T1 INNER JOIN Keyword AS T2 ON T1.episode_id = T2.episode_id WHERE T1.title = 'Shield'
database name:db_id law_episode
Episode table Episode Cols: episode id dtype text, series dtype text, season dtype integer, episode dtype integer, number in series dtype integer, title dtype text, summary dtype text, air date dtype date, episode image dtype text, rating dtype real, votes dtype integer, 
Keyword table Keyword Cols: episode id dtype text, keyword dtype text, 
Person table Person Cols: person id dtype text, name dtype text, birth date dtype date, birth name dtype text, birth place dtype text, birth region dtype text, birth country dtype text, height meters dtype real, nickname dtype text, 
Award table Award Cols: award id dtype integer, organization dtype text, year dtype integer, award category dtype text, award dtype text, series dtype text, episode id dtype text, person_id dtype text, role dtype text, result dtype text, 
Credit table Credit Cols: episode id dtype text, person id dtype text, category dtype text, role dtype text, credited dtype text, 
Vote table Vote Cols: episode id dtype text, stars dtype integer, votes dtype integer, percent dtype real, 
