Cliff notes:
1) Jockeys pulling back the reins, fixing races.
2) Jockeys giving key-info to bettors.
There's one KEY note to contemplate re: this clip. This is English horse-racing. Someone can clarify this for me. But here's the KEY: a good % of English horse-racing is done on a FIXED-odds basis.
IE, it's not a tote-board. If horse3 is 3/1, those are the odds. Doesn't matter if $1Mill bets come in the last minute b4 post.
In USA, the same $1Mill bet would drive the tote-board odds way down.