Vert is running a fever in this cartoon. Instead of the standard thermometer, he has in his mouth a neurocalometer. This is an instrument that some chiropractors use to detect irritated nerves brought about by vertebral misalignment (subluxation). The two heat sensitive probes are run on either side of the spine, taking the “temperature” of the skin. If there is a difference in temperature between sides, a subluxation likely exists at that level.
Joke Decoder (panel 34)