Venefica

he didn't have any older siblings (that we know about) to borrow clothes from, which was why he was in his parents' clothing; the fact that he wasn't loaned any clothes that fit marginally better or were even for boys from the neighbours suggests that the Snapes weren't particularly close to the other families, and i expect a large number of flies in the house (enough to be shooting down, enough to spot when harry only saw the memory fleetingly) suggests poor sanitation in the home

It's not just a case of Bellatrix being judgy about a Muggle neighbourhood, currently falling apart with houses on the cobbled streets boarded up and with broken windows, and a dirty, smelly river; Snape's home growing up was considered "a poor recommendation" even when he was a child. Two up, two down houses were, in that period (and even before) often falling apart, known for being unsanitary and unsafe, as well as damp and cramped together. they were never intended to be nice; they were thrown up so that workers could be near the factories, and that was about the only concern at the time

There's some really vivid descriptions of living in these sorts of houses around, but I've just found this one from facebook (with images I've added from flashbak.com):

The house had no electric supply and relied solely on gas for everything.

One wall in each room had one gas mantle fitted to it for light and when the mantle became faulty it would smell and the light would become less bright and eventually cease to do the job and need replacing.

There was a coal fire grate in each room but only the living room fire was kept lit to keep the costs down because although people worked long hours wages were low and money was in short supply.

In the kitchen the heat from the stove when cooking provided some warm that also made its way upstairs into the bedrooms.

During the winter months when the house was particularly cold overcoats were placed over the blankets on the beds for extra warmth for the children in the front bedroom. While the parents slept in the smaller back bedroom.

There was only one water tap in the house situated in the kitchen and the kettle or pans had to be filled when hot water was required. They were heated on the stove and because there was no bathroom the young children were washed in the large sink or a tin bath while others went to the public baths situated nearby, local to the area.

The toilet was in the back yard and was also unlit, leaving the gas light from the kitchen to light up the yard through the window.

Toilet paper was old newspapers that had been cut up into squares and made ready for use.

All flooring in the house was covered with lino with the exception of the living room that had a rug in the centre for comfort and to help prevent wear and tear. Since the end of the world war II there had been shortages and many households struggled to get basic food stuff and clothing.

The black market had been active for some years and those that had the money would get what they needed, while for those that had little depended on the rationing system introduced by the government to make sure that everyone got at least basic food stuff.

The I.D. card had been introduced because of the war and was proof of who you were and was used for the benefit of rationing. There were often queues at the butchers and many families got the scrag ends and scraps that were left over.

When it came to clothing, families would put aside what was worn by one child until the next child had grown enough to wear them and every item including shoes were cleaned and repaired if possible and put away and saved for later use.

In those days children at play preferred to play outside and regularly would play along the canal and the neighbourhood streets and alleyways. There were very few cars around and despite the unclean air from the surrounding factories they would play all day outside until they were called in.

In those days there were very little restrictions on pollution and it was normal to wake up in the mornings to smog that sometimes lasted all week. A real pea souper as they say

but like... imagine snape growing up there, like that, with no sense of community and parents who couldn't afford to or weren't able to care for him properly. this is so far beyond 'weasley poor' with their warm, cosy home and plenty to eat; this is gaunt poor, improper housing, and conditions that regularly made people ill

perhaps the Snapes had to rely on the black market to even eat enough, if they could afford it; I'm picturing chest infections and frost on the insides of the windows over the winters, and flies crawling in the house in the summers - and apparently limited use of magic at the time snape was growing up to rectify any of it, else the descriptions wouldn't be so consistently negative (and evocative) with a potential swarm of flies in his bedroom

(wonder if he was underage here, and using his wand since his mother would've had one, or whether it's a snippet of post-hogwarts snape; the next memory is of snape on a broomstick, so presumably that's at hogwarts, and he was underage in the fly memory, trapped/hiding/sulking in his room)