pop (something) in/into something
infml— phrasal verb with pop us/pɑp/verb -pp-
(MOVE QUICKLY)
to put something quickly into something else:
Pop the CD-ROM into a personal computer.
Just pop your supper in the microwave.
pops into your head/mind
Something that pops into your head/mind is an idea that you suddenly have:
He jotted down story ideas that popped into his head.