Judi Miller couldn't determine the source of the smell, but when she pulled up the floor mats, she found maggots.
She said she found a nest in the air cabin filter.
"It's like a dirty diaper that's been sitting and festering for months," Miller said. "It was just the most disgusting thing."
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Mechanics went high-tech by using a tiny camera to search inside the dash, where they found a dead mouse.
"This is not a 'Stuart Little Christmas Story' right here," the mechanic said. "It was horrific for all of us."
Mechanics said you should keep your windows up when parked to avoid an infestation.