Detection of dead body in insulation

[Thundagere]

Strange title? Basically, a few days ago we got a dead rat in our ceiling, which is covered in insulation. Took a while to find it, but it got me thinking, how would you detect a dead rat body?
If it recently died, I first thought you could use thermal imaging (aside from the expensive aspect), but then I realized that the insulation would reflect the heat of the body and make it difficult to pinpoint. Trying to track gases with some sort of electronic nose is pretty expensive and difficult. ANy ideas on this? It's not really something important, but I was just wondering.

 

[Khashishi]

from the smell

 

[mfb]

Without special equipment?
Find some animal which can detect the smell (dogs, humans, ...).
Find holes in the insulation and follow them.

With special equipment?
X-rays, neutrons, NMR, basically every imaging technique which allows to give some sort of contrast.

 

[Thundagere]

Could you give me some background info on how NMR would work?

 

[mfb]

If parts of the insulation are not too big and movable, put them in a scanner and try to find deviations in the images. I would expect that rats have a different amount of hydrogen in their body, and a different chemical composition. If some rat-shaped structure appears, you found the rat.
For the physics of NMR, see wikipedia, books or whatever.