worm
The professor opened a can of worms by saying that alcohol is more dangerous than cannabis or ecstasy.
This interview has opened up a whole new can of worms.
What can of worms had he opened?
Questioning a belief like this opens up a whole can of worms about questioning other beliefs.

SMART Vocabulary: related words and phrases

Causing difficulties for oneself or others
ask questions of someone/somethingidiom
be a tall orderidiom
be asking for troubleidiom
be your own worst enemyidiom
bother someone with something
catch
dig
make heavy weather of somethingidiom
make it difficult for someone to do something
obduracy
overburden
pitchfork someone into something
sand
shoot
subject someone/something to something
sucker punch
swamp
tall
throw sand in the gearsidiom
wrong-foot