TIL wheatstone bridges are actually quite cool

a wheatstone bridge is able to pick even small changes in resistance on very low-current systems (e.g. plants). so a clip which is measuring/dividing voltage on a leaf is able to detect even micro-amp changes by breathing.

http://cargocollective.com/gutonobrega (Projects: Breathing / Equilibrium)

Wheatstone-bridge-1

http://www.1010.co.uk/org/biologic.html