godan verb (-ru), intransitive verb
be covertly swapped; be replaced (e.g. with a counterfeit)
Describes something being secretly or deceptively exchanged for something else, often with a negative connotation of trickery or substitution.
本物の宝石が偽物にすり替わっていた。
The real jewel had been covertly swapped with a fake.
いつの間にか中
The contents have been switched without anyone noticing.