Why "pass" object goes to vcl_hash?

[Kelvin Loke]

This was bothering me for quite some time. I looked through the Varnish
Book detailed request flow diagram, an object that is "pass" in vcl_recv()
will go straight to vcl_pass() -> vcl_fetch() -> vcl_deliver().

But the varnishlog below tells me otherwise, why an object that is "pass"
in vcl_recv still needs to go to vcl_hash()?

   34 ReqStart     c 1.1.1.1 39816 1065872559
   34 RxRequest    c POST
   34 RxURL        c /marina/s/CheckSession
   34 RxProtocol   c HTTP/1.1
   34 RxHeader     c Host: localhost:8082
   34 RxHeader     c Accept: text/plain, */*; q=0.01
   34 RxHeader     c Origin: http://localhost:8082
   34 RxHeader     c X-Requested-With: XMLHttpRequest
   34 RxHeader     c User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64)
AppleWebKit/537.22 (KHTML, like Gecko) Chrome/25.0.1364.152 Safari/537.22
   34 RxHeader     c Referer: http://localhost:8082/member/w.aspx
   34 RxHeader     c Accept-Encoding: gzip,deflate,sdch
   34 RxHeader     c Accept-Language: en-US,en;q=0.8
   34 RxHeader     c Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
   34 RxHeader     c Cookie: JSESSIONID=5651fba1110cfdd2edf035494eec;
sl=-1237168048
   34 RxHeader     c Connection: close
   34 RxHeader     c Content-Length: 0
   34 VCL_call     c recv
   34 VCL_return   c pass
   34 VCL_call     c hash
   34 Hash         c /marina/s/CheckSession
   34 Hash         c
   34 Hash         c
   34 VCL_return   c hash
   34 VCL_call     c pass pass
   34 Backend      c 26 member_micro member_micro
   34 TTL          c 1065872559 RFC 0 -1 -1 1364453898 0 1364453897 0 0
   34 VCL_call     c fetch
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