Yeah, they do that

*ahem*

Not to paint all guys with a chauvinistic or testosteronic brush, but ... um... stallions are guys - big balls and testosterone and all that stuff, and, (cover your eyes if you have a delicate constitution) they masturbate. a lot. and there is a reason that 'hung like a horse' is a compliment.

That's because, well... because they're 'well hung' - at least as long and most probably thicker than your heroine's arm.

so if your virginal heroine rounds the corner at just the right time, she's likely to get an education. Stallions stand around having pleasant dreams at all hours of the day. He may just be dropped and engorged or he may be happily bouncing it up and down so it thumps on his belly. They aren't shy. ('they' meaning stallions, not heroines. ... heroines can be shy)

and that nice sized puddle by the gate that looks like semen ... it's probably semen. If your heroine doesn't know what semen looks like, the puddle of stuff that looks vaguely, but not exactly like mucus - it's semen.

No picture on this one. ... (but it should be easy enough to google.)

Sue L