Horses worry me, that much brainless muscle is scary.
I have found that the riders are not always sure how the horse(s) will react and if it is the machine or flag causing the problem.
eg I came up to a group of 4 horses on a quiet road, called/whistled got the last riders attention asked if it was alright to go by, he said fine no problem, horses good.
2 of the horses took off as if a rocket had been shoved up their arses.
If approaching from behind, I will slow down, call/whistle/talk and not pass until I have been seen by the riders/handler
If approaching the front I will slow down, ask if they want me to stop/remove flag.
However if after a number of these, if there is a distinct lack of goodwill/roadsense (I have been told I should not be on the road) then the time spent on these is reduced
The "fun" thing about a recumbent trike is if you cycle across dartmoor then all the wild ponies, which have been ignoring the traffic, scatter like mad.
It the same with the wild ponies in the new forest, deer in scotland and even reindeer in Iceland .....
I've done this to pigs in Norfolk, and seen them try and go from lying to flat out run from a wallow