I'm starting to doubt my understanding of English

I hope this is just a misunderstanding of horse racing (I am not familiar with this topic at all). I understand 1 and 2, as for 3, this is a description of how the odds on horses change depending on the results? Well, like if a boxer loses his first fight to an underdog, then his odds for the next fight change and he himself can become an underdog. Right?
Yes, but they change even if it's not the same boxer

So you have two horses with the same pedigree, same trainer, same jockey, same odds, in two consecutive races, if the first horse is a flop and a total failure, the second one will jump in odds a ton.
Now if you want to hear somethign funny, there was a race in which the fences were damaged in the previous race, the sun was at a bad angle so
instead of 12 or 14 fences they had to jump only 2, the rest would be bypaseds, a horse that was 4x to 5x in the morning became favorite because he was speedy but he was bad at jumping, and, yeah, it won!!!! despite nearly falling at one of the only two fences he had to jump

Overall, quite interesting information, as I already said, I am not familiar with horse racing and betting on it at all. Now it is clear why this sport has its own stable audience of fans.
In your opinion, does increased volatility in odds give betters a chance to use it somehow? Or do bookmakers take a big margin because of this? I remember checking men's and women's tennis and in women's (where volatility is always higher) the bookmaker's margin was on average 8% (a couple of percent higher than in men's).