Create RULE AS ON SELECT when some field is in expression?

Question

I want to log SELECTS when some exact field is in the statement. Eg. I have table "transactions" where are about 20 fields. But I want to call rule (really -- to log that select) only when someone includes the field "body" in the query, does not matter if with others fields or not.

Like that:

CREATE OR REPLACE RULE log_selects_body AS ON
  SELECT TO transactions WHERE -- I don't know what to write here
  DO ALSO RAISE DEBUG 'Body was accessed';