Capacitive touchscreens can be tricked into recognizing touches from various sources using electrically conductive material. This is how a simple touchscreen stylus works.

However, this works with all kind of electrically conductive material, and it doesn’t need to be as conductive as metal. Fresh muffins, for example, contain enough humidity to be electrically conductive and can therefore be used to create a tangible that generates three unique touches on the screen. These touches can then be used to identify the tangible on screen and use it as an input controller.

In the media

https://www.deutschlandfunknova.de/nachrichten/zukunftstechnologien-was-macht-der-muffin-auf-dem-screen

Publications

• F. Heller, “Muffidgets: Detecting and Identifying Edible Pastry Tangibles on Capacitive Touchscreens,” in Proceedings of the Fifteenth International Conference on Tangible, Embedded, and Embodied Interaction, New York, NY, USA, 2021.
  [Bibtex]

  @inproceedings{heller2021a,
  address = {New York, NY, USA},
  author = {Florian Heller},
  booktitle = {Proceedings of the Fifteenth International Conference on Tangible, Embedded, and Embodied Interaction},
  doi = {10.1145/3430524.3442449},
  isbn = {978-1-4503-8213-7/21/02},
  keywords = {tangibles, capacitive touchscreens, baking, pastry},
  location = {Salzburg, Austria},
  numpages = {6},
  publisher = {Association for Computing Machinery},
  series = {TEI '21},
  title = {Muffidgets: Detecting and Identifying Edible Pastry Tangibles on Capacitive Touchscreens},
  url = {https://doi.org/10.1145/3430524.3442449},
  year = {2021},
  bdsk-url-1 = {https://doi.org/10.1145/3430524.3442449}}