I'm sorry to hear about your snake escaping and I hope your snake still turns up, Hipporex. It is a reptile so even after a week it not impossible he could still be alive and might still turn up somewhere. So I wouldn't give up hope yet. I don't think I can offer any help, but I do believe that snakes like warm and moist spaces as well as small hiding spaces.
I unfortunately have had two escapes with chickens. Both happened with my Brabanter chickens that I have had since 2015. The first happened in the fall of that same year and concerned the rooster of my 1.3 potential breeding flock.
Now these Brabanters are (or certainly at the time were) much more stressy and flighty chickens than I've had before, and this breed is also slimmer built and much better at flying than your average chicken. The rooster got out when I stupidly let the gate open just a bit during feeding, alongside with one of his hens, which I ended up plucking out of patch of stinging nettle, at my own expense, of course - it was quite warm and I was wearing a T-shirt with short sleeves - and I would say deservedly so. The rooster however, I had to give up on after hours of searching the stinging nettles, brushes and corn field behind our yard. I did see him again the next morning, flying away about as well as any wild gallid bird would have, and didn't think I would ever see him again.
I got real lucky though that time, as eight days after the escape our two houses down the street neighbor noticed the rooster running around the yard of his family's farmhouse and was able to lure the (probably hungry) rooster into a shed with pigeon feed, then catch him and put him in a box to return him.
In 2017 I had another case that likely happened in much the same way, although this time with offspring (one and probably only time I bred them) of my Brabanters. I didn't even notice the escape in this case until I found one of my young hens (fully feathered and independent from the foster hen at the time, but still with plenty of growing to do) missing later on, and I never fully found out what happened, so I'm only going by a likely scenario here. This time I wasn't quite so lucky and I never found the hen again, she likely fell prey to one of the neighborhood cats (she was well within the prey size range of a domestic cat) or perhaps some bird of prey (we do have sparrowhawks and buzzards in the area where we live).
I have been much more careful with the gates since, especially around my Brabanters (and they have admittedly calmed down a bit since), but there have been a couple more accidents (mostly mistakes in closing gates, followed by wind blowing them open) since, luckily all of them were quickly solved.
Mistakes do happen, even around pet animals, and as we are all (presumably) still human, we cannot prevent every last one. As long as there isn't deliberate cruelty or neglect of essential prevention measures, we shouldn't continue to beat ourselves up about these.