trouble when REVOKE

The ORACLE user "hee" was created by "DBA". The only privilege "hee" has is "CREATE SESSION":

        hee%SQL> select * from session_privs;

	PRIVILEGE
	-------------------
	CREATE SESSION

But somehow I still can SELECT and MODIFY tables created by another user, say, "head".

        hee%SQL> select * from head.branchdb;

	BRANC NAME  LOC 
	----------------
	CHASE MANH  NYC 

[And I got the same result when running: SQL> select * from branchdb.]

When trying to revoke this privilege from "hee", I got the following message:

        head%SQL> revoke select on branchdb from hee;

	revoke select on branchdb from hee 
	ERROR at line 1:
	ORA-01927: cannot REVOKE privileges you did not grant

I got the same error message when doing the same as "DBA".

	SQLDBA> revoke select on branchdb from hee;
	ORA-01927: cannot REVOKE privileges you did not grant

When I created a table from user "head", I was successful to REVOKE the SELECT privilege on the new reated table from "hee". How come I cannot do so on those tables, such as "branchdb", which were existing before the user "hee" was created?

Thanks for help.

Ed HE

-- 
Enhua E. HE
4 Washington Place, #99 
New York, NY 10003
Email: eeh0063_at_is2.nyu.edu