When repeated, a nonverbal "Can you hear me?"

TAP

Think of the sound you might make to quietly get someone's attention, like knocking gently on a table or shoulder.

The clue hints at the word "tap" because when you repeat it—"tap tap"—it mimics the sound someone might make to get another person’s attention, like knocking lightly to ask, "Can you hear me?" without speaking. It’s a playful way to turn a simple action into a nonverbal question, relying on the idea that tapping is a universal gesture for checking in or signaling someone. The answer itself is short and fits neatly into crossword grids, making it a clever little wordplay.