A questioner said:
What is this iron thing installed into the wall of my late-Victorian house?

Some of the answers here:

1. It’s a hose bib handle someone used as an air vent by mortaring it in. The contemporary equivalent would be an “Air Brick” – the purpose is to prevent condensation from building up in the void between the outer brick and the inner layers of the wall, leading to the breakdown of the mortar. Given the climate of England, preventing dampness in wall voids is important. Given the history of England in the last century, it’s likely someone had to be handy in a time of scarcity, and improvised in a clever way.
2. It’s unlikely there’s a void in the wall – construction in Britain during this period typically used solid walls.
3. That’s assuming the house is entirely late Victorian, and even during the later part of the 19th century, cavity walls did exist.There’s also two different compositions of bricks and mortar in this photo alone, implying that work was done in stages or it had to be rebuilt. If this house is near Liverpool or Manchester, it may have also been damaged during the 1940s, at which point cavity walls were fairly standard (and even preferred, because of the demand for building materials).
4. Looks like a fancy weep hole.
5. It looks like a hose bib (faucet) handle, but in the event that it is, I have no idea WHY it was put there, other than maybe to be used as a vent cover of some type.
6. 

7. This small (10cm wide) possibly iron flower like thing is about 1m above ground. My house is in North West England and was built in the 1890s, it is a former shop, and this is on the side wall (i.e. away from what was the shop entrance). There is no visible outlet on the inside.

8. There are marks going down the wall on the wall to the right that seem to indicate there was some other building or something connected to the wall, a green house or potting shed other type of building
9. and it works as a mouse stopper
10. Would it though? The gaps are pretty big. Google says mice can get thru a 1/4” hole.

What do you think about it? Let us know in the comment!