I smell dead things

It was a Monday evening and time to head home. I tripped merrily to my car which was parked in the basement of the building that houses my office. Actually, I have never tripped merrily anywhere, the only tripping I have done is the kind that ends with my nose touching terra firma firmly, but I have always wanted to trip merrily, so in this story I shall. My merry tripping came to an abrupt halt some distance from the aforesaid vehicle. The ghastly smell of decay was in the air. I peered around the dim crevices of the basement trying to spot the carcass. My investigation was brief as by now I was holding my breath and was not keen to risk keeling over. Secure in my car, I turned on the air conditioner as high as it could go and high tailed it home.
Cut to early Tuesday morning. I approached my four wheeled friend again, this time with the object of getting to work. Needless to say, I tripped along merrily. And there it was again. The stench of gruesome murders too long undiscovered. Let me tell you that few things put a kibosh on merry tripping as effectively as an assault on your nose by things long dead, but dreadfully unburied. While I reeled in disgust, I also did some quick thinking. The result of the quick thinking was this: it was mightily suspicious that both parking lots - home and office - smelt so disgustingly alike. I therefore proceeded to feel mightily suspicious and set off to work with a cloud of distrust above my head. The wheels kept turning, Sherlock-like. What were the common factors between Monday and Tuesday? The car and me. And I was pretty darn sure that I wasn't a zombie nor was I wont to carefully preserve dead rats in my pockets. That left a single prime accused.
On Tuesday evening when the evil odour persisted and all merry tripping was out of the question, I knew I needed help. I called a friend and said a sentence I never imagined I would be called upon to say, "I think there's something dead in my car". Later that night, armed with torches, we strip searched the car and found a big fat nothing. In the face of the snickering disbelief of my so-called friend I stuck to my guns. We decided to explore the engine. We stuck the light hither and non, in places were no light was meant to be stuck and then, suddenly, my light lit upon a staring eye. I shrieked, outdoing eight women in simultaneous labour.
Here is what we discovered, nestled cozily in my engine - the head of a fish, a tiny bone (but not that of a fish), and en empty packet that used to contain bread in days bygone. This is going to be one of the great mysteries of my life.