FOLLOWING DEICING; A B737-500 TKOF WARNING HORN SOUNDED WHEN THE THRUST LEVERS WERE ADVANCED FOR TKOF. THE CREW REJECTED THE TKOF AND FOUND THE PITCH TRIM OUT OF THE GREEN BAND. RESET TRIM.

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WE PUSHED BACK ON TIME AT XA:55Z TO DEICE (LIGHT SNOW FALLING; TXWYS IN GOOD CONDITION) AND MAKE A WHEELS UP TIME OF XB:21Z. DEICE WAS RELATIVELY QUICK AND UNEVENTFUL FOLLOWED BY A LONG SINGLE ENG TAXI DOWN RWY 33; TXWY F4; AND TXWY H TO RWY 23. WE STARTED THE #1 ENG AND RAN THE BEFORE TKOF CHKLIST WHEN IT WAS APPARENT WE WOULD GET RIGHT OUT. WE WERE CLRED FOR TKOF; RAN THE ENGINES UP IN ACCORDANCE WITH COLD WX OPS PROCS; RELEASED BRAKES AND THE CAPT PUSHED THE THROTTLES UP FOR TKOF. THE TKOF WARNING HORN SOUNDED ALMOST IMMEDIATELY AFTER BRAKE RELEASE SO WE TOLD TWR WE COULDN'T TKOF AND CLRED THE RWY. IN CHKING THE TKOF WARNING HORN ITEMS WE DISCOVERED WE HAD NOT RESET THE TKOF TRIM INTO THE GREEN BAND. WE SET THE TRIM; RE-RAN THE BEFORE TKOF CHKLIST; COORDINATED FOR A NEW RELEASE TIME; AND TAXIED BACK FOR TKOF. THE REMAINDER OF THE FLT WAS UNEVENTFUL. CONTRIBUTING FACTORS WERE MULTIPLE RWY XINGS AND FREQ CHANGES; SOMEWHAT COMPLICATED DEICE PROCS AT CYYZ WHICH BOTH OF US HAD NOT ACCOMPLISHED BEFORE; PERCEIVED TIME CONSTRAINT FOR RELEASE; CONFIGURATION OF ACFT COMBINED WITH STARTING SECOND ENG. SUGGESTION: SHOULD WE MAKE BEFORE TKOF CHKLIST READ LIKE THE MCP LINE; THAT IS: TRIM; WEIGHT; SPD; AND THEN VERBALIZE THE FLT SPECIFIC NUMBERS? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS ACTING AS THE FO ON THIS TRIP. HE STATED THAT HIS AIRLINE SAFETY REP HAS CALLED HIM ABOUT THIS; SEEKING THE CIRCUMSTANCES AND HIS INPUT FOR A SOLUTION. HE DOES STATE THAT A CHKLIST CHANGE COULD REQUIRE A VERBAL RESPONSE SUCH AS: TRIM; WEIGHT; AND SPD THAT WOULD MIMIC AN FMC DATA LINE. A B737 CHKLIST COULD READ: RECALL; FLT CTLS; TKOF DATA; FLAPS; STAB AND TRIM; TKOF BRIEFING; FLT ATTENDANT; START SWITCHES; AND XPONDER. THIS CHKLIST WOULD ONLY BE COMPLETE FOLLOWING ALL OTHER PROCS AND IMMEDIATELY PRIOR TO TAKING THE RWY FOR DEP. SUPPLEMENTAL INFO FROM ACN 640752: THIS IS WHEN WE NOTICED THE TRIM STILL SET FOR THE DE-ICING OP. WE ONCE AGAIN RAN THE BEFORE TKOF CHKLIST; CORRECTING THE TRIM AND GOT BACK IN LINE FOR DEP. I AM ALWAYS VERY CAREFUL ABOUT CHKING THE TRIM; BUT SOMEHOW WE BOTH MISSED IT THIS TIME. I GUESS WE SAW WHAT WE EXPECTED TO SEE.