“Girls, do you detect that musky, husky bison aroma?
Your mother is home! Now, go and rub her hooves.”
When you are doing your preflight checklist you set the autobrake switchto RTO. (Rejected Take Off)
When you start your take off roll if anything happens (like hitting a cow) that slows you down below V1 (decision speed) you hit the brakes and it automatically applies full braking .
If you are above V1 you take off, because if you try to stop you will run out of runway