Compile php4 beta 3 with --enable-force-cgi-redirect.
Attempt to access /cgi-bin/php directly.

Instead of the "Security Alert!" HTML document being returned, php will exit on signal 11.

Here's the backtrace:
$ gdb php.old php.old.core 
[snip]
Core was generated by `php.old'.
Program terminated with signal 11, Segmentation fault.
Reading symbols from /usr/lib/libm.so.2...done.
Reading symbols from /usr/lib/libcrypt.so.2...done.
Reading symbols from /usr/local/lib/libpng.so.3...done.
Reading symbols from /usr/lib/libz.so.2...done.
Reading symbols from /usr/local/lib/libintl.so.1...done.
Reading symbols from /usr/local/lib/mysql/libmysqlclient.so.6...done.
Reading symbols from /usr/local/lib/libjpeg.so.9...done.
Reading symbols from /usr/local/lib/libtiff.so.4...done.
Reading symbols from /usr/local/lib/libpdf.so...done.
Reading symbols from /usr/local/pgsql/lib/libpq.so.2...done.
Reading symbols from /usr/lib/libreadline.so.3...done.
Reading symbols from /usr/lib/libhistory.so.3...done.
Reading symbols from /usr/lib/libtermcap.so.2...done.
Reading symbols from /usr/lib/libpam.so.1...done.
Reading symbols from /usr/lib/libc.so.3...done.
Reading symbols from /usr/libexec/ld-elf.so.1...done.
#0  0x0 in ?? ()
(gdb) bt
#0  0x0 in ?? ()
#1  0x8073fec in php_body_write (
    str=0x80fb097 "<b>Security Alert!</b>  PHP CGI cannot be accessed directly.\n\n<P>This PHP CGI binary was compiled with force-cgi-redirect enabled.  This\nmeans that a page will only be served up if the REDIRECT_STATUS"..., 
    str_length=933) at output.c:148
#2  0x806005e in main (argc=1, argv=0xbfbfda30) at cgi_main.c:268
#3  0x805fd51 in _start ()