Some years ago I dropped a wagon off in Chard one hot summer Monday & was holding out my tacho disc for a lift back to base - (as we used to do once upon a time)
Artic with tipping trailer stopped for me & I jumped in to a steaming hot cab, I asked him why he didn’t have any windows open, he said “Wait a minute and I’ll show you”, eventually a box trailer overtook & he opened the window, the back draft sucked in the most god awful smell from the trailer - “Thats why I have the windows closed”
He picked up the remains from the slaughter houses for somewhere in Lincolnshire where it was rendered down for things like OXO cubes.
He reckoned summer Monday’s were worse as the offal & remains had sat in the yard over the weekend fermenting and gathering maggots.
Not a job for the fainthearted or vegans