Slipped

The spy slipped the secret code into the message, without anyone realizing it.

The secret plan was slipped into a confidential memo, without anyone noticing.

The papers slipped out of the folder and scattered across the desk.

The water level slipped as the drought continued.

I slipped up and forgot to send the important email.

The economy has slipped into a recession due to the pandemic.

The spy slipped past the guard and entered the building undetected.