On one occasion my Mom was helping me clean the corral of my mare and her 3 month old colt. I happened to be facing My Mom as she stooped over to shovel up a pile of manure. I could see the foal approaching her from behind and knew that he was a playful sort and that he might try something. But I was worried that if I warned my Mom she would turn around and get hit in the face with a hoof. So I watched in horror as my foal’s forelegs slid down either side of her head. She straightend up very fast!
Actually, no, and quite frankly, I could use the confidence boost.
This is funny, because my friend and I DID have a very similar conversation, in which we imagined what it would be like if that happened to humans.
I’m sure it was the Bohemias talking. 
(Emphasis added.)
Um, your “the penis”? What are you saying here?
My male Shiba Inu (a breed known for their “dignity”) used to have a crate pad he liked to play with. He had it up on my bed ripping it to shreds as usual when I guess he got a little turned on by it. I walk into the room and see him going to town on this thing. He’s so focused on it that he doesn’t notice that he’s about to back himself right off the bed - did I mention it was a very high bed? So I waited because I figured it was going to be worth it.
<THUMP> He’s on his back on the floor covered by the crate pad.
BWAHAHAHAHAHAHA!!! with much finger pointing.
He was not amused. I haven’t seen him hump anything ever again - at least not in my presence. I train em with shame. 
Ever seen an aroused Shamu (or whichever killer whale was the male)? I have. Nothing like your first glimpse of one of them swimming by at eye level and having it roll to expose it’s underside which is bearing an extremely large erection. Good times.
Also, giant tortoises are quite vocal. And the male ones are quite persistent.
A few years ago, my friend’s standard poodle developed a little crush on me. Unaware of Barnaby’s feelings for me, I mistakenly bent down in front of him. Next thing I knew, I felt paws on my hips, and he bore me right to the floor and started humping away.
Naturally, everyone else at the party was laughing too hard to help me for several minutes. All I recall saying was “Somebody please help me before he finishes!!!”
After he’d been pried off me, Barnaby actually licked my cleavage by way of thanks. I’ve known men who weren’t that considerate.
We were at the Houston zoo last year, by the elephant exhibit. Oh. my. God.
This one big male started slowly moving his butt from side to side. Gently shifting his weight from hind leg to hind leg. He started to get an erection! Swaying back and forth, getting larger by the minute. Hung like a horse? Try hung like a freakin’ elephant! It was HUGE! Back and forth, back and forth. Parents were herding their young children away. “Mommy, what is that elephant doing?”
Then he raises his tail, takes a huge dump (still wiggling) and then stops moving. I was laughing so hard, I couldn’t tell if he, uh, let loose… Then he wandered back to the barn, and the show was over.
Totally bizarre.
[The Knack]
“Muh-muh-muh-MY THE PENIS!”
[/The Knack]