query

i'm migrating from pypgsql to psycopg, and psycopg has an issue with 
this query string.

curpg.execute("""SELECT till_name,till_float
   FROM till_config
   JOIN transactions
   USING (id)
   WHERE for_venue = %s""",(Venue))

the error is as follows

psycopg.ProgrammingError: ERROR:  syntax error at or near "Cow" at 
character 102

SELECT till_name,till_float
       FROM till_config
       JOIN transactions
       USING (id)
       WHERE for_venue = Mad Cow

now i understand why it's erroring on that sql, but why isn't psycopg 
quoting it for me?