Help me locate this smell

[Grunt1ed]

In my sons bedroom it smells like a decaying fish (gone off prawns type of smell) it’s got worse over the last day or so. I’ve pulled everything out and can’t find the source. It smells like it could be coming from the walls. What could it be and how can I get rid of it?

If you have birds nesting in the roof, could be the smell of bird shit building up. ( voice of experience)

The cat once brought in a tiny dead shrew and stored it under the lino in the cupboard under the stairs. The smell was overwhelming for such a tiny creature. Can't remember if it smelled like gone off shrimp - think it was more foul cheese but could be a small creature. Check cupboards and under carpets.

@dementedma

If you have birds nesting in the roof, could be the smell of bird shit building up. ( voice of experience)

We have in the past had birds nesting in the roof, I’ve not seen them this year, but I’ve been occupied with other things, so could have been there.

I have a feeling I’m going to have to pull up the floor boards at this rate

The smell of a dead mouse is horrendous. You'll know it's something dead if the flies arrive next. You can get them in the wall cavity as well as under the floor.

We’ve arranged for someone to come out tomorrow, he said it could be a baby bird that’s fallen into the cavity. If that’s the case he can spray it with some chemical to get rid of the smell. It’s always on a weekend lol

Does sound like a dead bird or dead vermin. That smell I would describe as starting off like when the sanpro bin hasn't been emptied for a while and gradually gets worse.