No, it's more likely a random event. DA's books were mainly about random events.

It's been 10 years since I read Mostly Harmless, so I have to admit I don't recall the scene very well. But it would be uncharacteristically dark (to me) for Adams to make the boghog Fenchurch.

As Smart Dalek says, Adams is all about the random events. It's hard to read too much into any of what happens, because he stuffs so many tangential and inconsequential bits into every story.

So I'm saying no. If it's anyone, it's Agrajag. (If you don't know who that is, don't follow the link -- you haven't read far enough yet.)

I guess what always made it jump out for me is that a few pages earlier he goes into great detail about the boghogs, making sure the reader understands how they communicate. Then he has a passage where a boghog desperately tries to communicate with Arthur. Agrajag would have just tried to kill him or run away, I think.

As far as it being uncharacteristically dark, the whole tone of the book is pretty dark and hopeless from beginning to end, even compared to some of the blacker bits in Adams' earlier works: the sinister new guide, Random's identity troubles, Tricia/Trillian's regrets and coldness, and let's not forget the ending, though I'm sure many have tried...

He goes into great detail about the lives of the swampdwelling mattresses of Squornshellous Zeta in Life, the Universe, and Everything, but it's not very consequential, either. And in the movie, much is made of the Jatravartids, who were a trivial aside in the books.

BTW here are the two passages in question:

"[The brochure] talked about the early years of settlement. It said that the major activities pursued on NowWhat were those of catching, skinning and eating NowWhattian boghogs, which were the only extant form of animal life on NowWhat, all other having long ago died of despair. The boghogs were tiny, vicious creatures, and the small margin by which they fell short of being completely inedible was the margin by which life on the planet subsisted. So what were the rewards, however small, that made life on NowWhat worth living? Well, there weren't any. Not a one. Even making yourself some protective clothing out of boghog skins was an exercise in disappointment and futility, since the skins were unaccountably thin and leaky. This caused a lot of puzzled conjecture amongst the settlers. What was the boghog's secret of keeping warm? If anyone had ever learnt the language the boghogs spoke to each other they would have discovered that there was no trick. The boghogs were as cold and wet as anyone else on the planet. No one had had the slightest desire to learn the language of the boghogs for the simple reason that these creatures communicated by biting each other very hard on the thigh. Life on NowWhat being what it was, most of what a boghog might have to say about it could easily be signified by these means..."

"As Arthur had left their offices he found he was trembling slightly. Not only had he lost Fenchurch in the most complete and utter way possible, but he felt that the more time he spent away out in the Galaxy the more it seemed that the number of things he didn't know anything about actually increased.

Just as he was lost for a moment in these numb memories a knock came on the door of his motel room, which then opened immediately. A fat and dishevelled man came in carrying Arthur's one small case.

He got as far as, 'Where shall I put-' when there was a sudden violent flurry and he collapsed heavily against the door, trying to beat off a small and mangy creature that had leapt snarling out of the wet night and buried its teeth in his thigh, even through the thick layers of leather padding he wore there. There was a brief, ugly confusion of jabbering and thrashing. The man shouted frantically and pointed. Arthur grabbed a hefty stick that stood next to the door expressly for this purpose and beat at the boghog with it.

The boghog suddenly disengaged and limped backwards, dazed and forlorn. It turned anxiously in the corner of the room, its tail tucked up right under its back legs, and stood looking nervously up at Arthur, jerking its head awkwardly and repeatedly to one side. Its jaw seemed to be dislocated. It cried a little and scraped its damp tail across the floor. By the door, the fat man with Arthur's suitcase was sitting and cursing, trying to staunch the flow of blood from his thigh. His clothes were already wet from the rain.

Arthur stared at the boghog, not knowing what to do. The boghog looked at him questioningly. It tried to approach him, waking mournful little whimpering noises. It moved its jaw pain-fully. It made a sudden leap for Arthur's thigh, but its dislocated jaw was too weak to get a grip and it sank, whining sadly, down to the floor. The fat man jumped to his feet, grabbed the stick, beat the boghog's brains into a sticky, pulpy mess on the thin carpet, and then stood there breathing heavily as if daring the animal to move again, just once.

A single boghog eyeball sat looking reproachfully at Arthur from out of the mashed ruins of its head.

'What do you think it was trying to say?' asked Arthur in a small voice."

I dunno, it just seems so ugly and brutal compared to other dark moments like this in Adams' work, that I still feel like there's something more going on than just a random incident.

I could copy and paste everything me3dia said, because it's been that long since I read it, and my assumption was the same as his.

I only read it once, though; the book was so depressing that it seemed to me like Adams was totally fucking sick of the universe he'd created--and sick of the attention it got--and wanted to just completely destroy it, once and for all.

What I don't get is "Young Zaphod Plays It Safe".

You don't get "Young Zaphod Plays It Safe" because most U.S. publications of the story omit a crucial phrase which is in fact the very punchline of the gag. The version of the story published in A Salmon of Doubt fortunately restores these words. You can read it here (you want the very last paragraph).

Another vote for Agrajag.