Rubberized tube with a capped probe protruding from the end and an electrical lead on the opposite end w/ alligator clip. The “probe” end has a bundle of doubled over fabric.

My title describes the thing. Found three of these at a thrift store. The cap attachment on the probe end has “Nalgene” written on it. Possibly an LED on the bottom of the rubber tube as well. Red, green, and yellow pieces protruding are rigid.