quick / slow on the uptake
/ˌkwɪk ɒn ði ˈʌp.teɪk/idiom
quick or slow to understand things
быстро / медленно соображающий
Uptake здесь — «схватывание», понимание. Часто в отрицании: She’s not exactly quick on the uptake.
“She’s very quick on the uptake — you only need to explain things once.”
“Sorry, I’m a bit slow on the uptake today.”
“Children are often quicker on the uptake than adults with new technology.”