This month's joke is based on the double meaning of the idiom put one's foot down:
1 - To put your foot down - To act firmly / To tell someone strongly that they must do something or that they must stop doing something:
"You can't just let him do what he wants, you'll have to put your foot down."
2 - To put your foot down - To drive faster. To press down harder on the accelerator (gas) pedal of your car:
"We're going to be late unless you put your foot down."