REJECTED TKOF BY A B737-700 FLT CREW WHEN THE TKOF CONFIGN WARNING HORN SOUNDS DURING A ZERO FLAP CONFIGN TKOF ATTEMPT AT BNA; TN.

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RWY 31 WAS REQUESTED PRIOR TO PUSHBACK AND WE EXPECTED THAT RWY BASED ON HEARING OTHER ACFT BEING APPROVED FOR IT. OPC DATA FOR RWY 31 WAS ENTERED. DURING PUSHBACK AND START; GND ADVISED UNABLE RWY 31 AND TO EXPECT RWY 20C. AFTER PUSHBACK; WE ACCOMPLISHED THE AFTER START FLOW AND CHKLIST. I THEN ASKED THE FO TO RUN THE OPC NUMBERS FOR RWY 20C. WE REVIEWED THE NUMBERS AND HE ENTERED THE CHANGES IN THE FMC. THIS IS WHERE THE ERROR OCCURRED. FOR SOME REASON; I THOUGHT WE WERE READY TO GO AND I ASKED THE FO IF HE WAS READY. HE SAID YES; CALLED GND FOR TAXI AND OFF WE WENT. NEVER CALLED FOR 'FLAPS 5 DEGS; PRE TKOF CHKLIST.' SOMETHING I HAD DONE THOUSANDS OF TIMES BEFORE. OUR ERROR WAS DISCOVERED ONLY AFTER HE ADVANCED THE THRUST LEVERS FOR TKOF. THE TKOF WARNING HORN SOUNDED AND AFTER CHKING THE STABILIZER TRIM TO BE NORMAL; I LOOKED AT THE FLAP INDICATOR AND REALIZED OUR ERROR. WE ASKED TWR TO EXIT THE RWY. WE PERFORMED THE PRE TKOF CHKLIST AND RETURNED TO THE DEP END FOR TKOF. LOGBOOK WRITE-UP WAS ACCOMPLISHED AND SIGNED OFF BY MAINT UPON ARR AT HOUSTON. I FEEL THAT THE PRIMARY CAUSE OF THIS EVENT WAS WHEN I ASKED THE FO TO UPDATE THE OPC AFTER PUSHBACK; THUS BREAKING THE FLOW FROM THE AFTER START CHKLIST RIGHT INTO THE PRE TKOF CHKLIST. MY THINKING WAS TO HAVE THE UPDATED NUMBERS DONE BEFORE TAXI BECAUSE THE V-SPDS ARE PART OF THE PRE TKOF CHKLIST. ALSO; IT WOULD ALLOW US BOTH TO BE 'HEADS UP' DURING THE TAXI. BUT I NEVER CALLED FOR THE CHKLIST. SOME CONTRIBUTING FACTORS ARE ATC ISSUING THE RWY CHANGE DURING THE PUSHBACK AND ENG START AS THIS NOW GOT MY MIND THINKING AHEAD ABOUT THE NECESSITY FOR NEW OPC DATA AND A NEW TAXI RTE. WE PUSHED ON TIME AND WERE NOT RUSHED. MY NORMAL MODE OF OP IS TO TAKE THINGS SLOW AND METHODICAL. I AM PROBABLY ONE OF THE SLOWEST TAXIING PLTS AT COMPANY. I HAVE ALWAYS THOUGHT THE CHANGE IN PROC TO DO THE PRE TKOF CHKLIST BEFORE TAXIING WAS A POSITIVE ONE. BUT SOMEHOW; ON THIS DAY; I MISSED THE CRITICAL ITEM. FORTUNATELY; THE LINK IN THE CHAIN OF EVENTS WAS BROKEN BY THE TKOF WARNING HORN. FROM NOW ON; I AM GOING TO MAKE SURE THERE IS CONTINUITY FROM THE AFTER START CHKLIST RIGHT THROUGH TO THE PRE TKOF CHKLIST. ALSO; I AM GOING TO WRITE THE WORDS 'FLAPS' AND 'CHKLIST' ON MY RELEASE AND DRAW A LINE THROUGH THEM AFTER THEY ARE ACCOMPLISHED AS AN ASSURANCE THAT THEY HAVE BEEN COMPLETED. SIMILARLY; AS I ALWAYS CHK FOR 5 GREEN LIGHTS PRIOR TO LNDG; I WILL BE CHKING THE FLAP AND TRIM INDICATORS WHEN I PUSH THE ATTENDANT CALL BUTTON PRIOR TO TKOF.