think on your feet
US /θɪŋk ɑn jʊər fiːt/
UK /θɪŋk ɑn jʊər fiːt/

1.
pensar con rapidez, reaccionar rápidamente, improvisar
to be able to think and react quickly, especially in an unexpected situation
:
•
A good salesperson needs to be able to think on their feet.
Un buen vendedor necesita ser capaz de pensar con rapidez.
•
When the unexpected question came, she had to think on her feet to give a suitable answer.
Cuando llegó la pregunta inesperada, tuvo que pensar con rapidez para dar una respuesta adecuada.