* A very soft, smooth cloth or microfiber: This captures the texture and suppleness of a tongue.
* A silicone spatula: Silicone can have a slightly rubbery, flexible feel similar to a tongue.
* A damp, warm washcloth: This captures both the texture and temperature.
* Certain types of textured or flocked materials: These might mimic the slight roughness of a tongue's surface.
* A very smooth, rounded stone, warmed by the sun: Temperature, smoothness, and natural origins all contribute to the comparison.
The best answer depends on what aspects of the tongue's feeling you want to emphasize!