imperceptibly (adverb)

1. The character tiptoed imperceptibly across the room, making sure not to wake anyone up.

2. Zeus descended to Earth imperceptibly, taking the form of a mortal to interact with humans.

3. The punchline of the joke was delivered imperceptibly, catching everyone off guard with its subtle humor.

4. In the science fiction novel, the alien's presence was revealed imperceptibly through small, subtle clues and hints.