Slipped

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

He slipped and used a curse word in front of his grandmother.

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

The building's safety standards have slipped over the years due to lack of maintenance.

The bird slipped out of its cage and flew away.

He slipped a piece of paper into the envelope and sealed it shut.

The crowd's noise slipped to a murmur as the speaker took the stage.

The mouse slipped through the small crack in the wall.

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