creep up
US /kriːp ʌp/
UK /kriːp ʌp/

1.
acercarse sigilosamente, subir poco a poco
to move slowly and quietly so as not to be noticed
:
•
The cat crept up on the bird.
El gato se acercó sigilosamente al pájaro.
•
Prices have been creeping up steadily.
Los precios han estado subiendo constantemente.