SCIENCE, TECH, WEATHER, KNOWLEDGE

as bright as a button (B2)

very intelligent and full of energy

get your wires crossed (B2)

fail to understand each other

it's not rocket science (C1)

something is not difficult to understand

a cog in the machine (C2)

a small member of a larger organization

a silver surfer (C2)

an old person who uses the Internet

blow a fuse/gasket (C2)

lose one's temper and become very angry

in layman's terms (C2)

in plain or simple language

oil/grease the wheels (C2)

help something go smoothly

reinvent the wheel (C2)

try to do sth that has already been done

the calm before the storm (B2)

a very quiet period before sth chaotic starts

save something for a rainy day (C1)

save sth for a time when it might be needed

be as pure as the driven snow (C2)

be morally perfect

get wind of something (C2)

find out about something secret or private

in the dead of winter (C2)

in the coldest time of the year

it never rains but it pours (C2)

misfortunes tend to follow each other

make heavy weather of (C2)

make sth harder or more laborious to do

steal somebody's thunder (C2)

prevent somebody from having success

throw/cast caution to the wind(s) (C2)

act in a completely reckless manner

be wise after the event (B2)

it's no use crying over split milk

a pearl of wisdom (C1)

a wise saying or piece of advice

drop a hint (C1)

suggest or ask for sth in an indirect way

a smart alec(k) (C2)

someone who always has the right answer

great minds (think alike) (C2)

two people have the same opinion

rack your brains (C2)

think very hard

shed/cast light on something (C2)

provide information about something