OED DEFINITION: RHUBARB - 4. a. The word ‘rhubarb’ as repeated by actors to give the
impression of murmurous hubbub or conversation.
4. d. slang. Nonsense, worthless stuff.
Garfield's expression pretty much covers it.
(Although in all fairness, I think some direct sunlight was falling on the sensor, so that bumped it up a little. And the temp was a bit cooler than 81 in the house because the windowsill was also in getting some sun.)