I've been re-reading the John Byrne/Ron Wilson 1980s Thing series, as a bit of a precursor to its Saturday Splash Page entry in a couple of months. In issue 3, Crystal and Lockjaw come looking for Ben, because Quicksilver is determined to expose he and Crystal's daughter to the Terrigen Mists, even though there's no telling what that'll do to a half-mutant/half-Inhuman child.
Crystal's opposed, but Inhuman society, among its other fucked-up policies, puts full control of that decision in the hands of the father. Even when the mother's a member of the royal family, and the dad's just some jackass that married into the society.
Ben and Lockjaw both step in, but what ultimately convinces Pietro to stop is when Lockjaw speaks, revealing that he's not just some mutated dog, but that his form is what the Mists did to him.
What I remembered recently was, in his first issue on X-Factor, Peter David had a scene where Jamie Madrox tries to talk with Lockjaw, because he heard from Ben Grimm about Lockjaw being able to talk. Pietro laughs and explains that was just Karnak and Gorgon using a microphone to have fun with Grimm, by making him think he found a kindred soul.
That's a weird way to reverse that. I get Byrne retconned Lockjaw in the first place, and Marvel certainly seems to prefer Lockjaw just be a mutated dog. But in-story, that's not the time where you play that sort of practical joke. A child's life is potentially on the line, and given Crystal's power, if Luna dies because of this, there's a decent chance a volcano erupts right under Attilian and kills everyone.
Doylist explanation #1: Peter David decided the Inhumans had enough dodgy shit in their society, with the Alpha Primitives and all, so dog-man was a step too far.
Doylist explanation #2: Peter David was just being kind of a petty dick. Not a stretch for the guy who put Rocket Raccoon in his Captain Marvel run as a throw rug, or who dismissed an appearance by Hulk and Doc Samson in Amazing Spider-Man (first part reviewed here) that did not appear to contradict his run in any way as a "dream".
Watsonian approach #1, Pietro's lying his ass off because that whole circumstance was him being wildly wrong and he doesn't want to cop to it. Karnak and Gorgon did it to trick Pietro, not Ben, as a last-ditch move to make him stop. Obviously Pietro isn't going to admit he endangered his only daughter's life because he couldn't bear the thought of her being "merely" human. Even if he likes to pretend he doesn't care what others think of him, it would probably help if his new teammates aren't all looking at him like something they'd scrape off their shoes.
Watsonian approach #2: Lockjaw can talk, but as Thing surmised in the first story, it hurts. He's sure as hell not going to spare any words for a dick like Pietro (who he's likely only too happy to get far away from everyone he cares about). Or simply to prove that he can to a slack-jawed gawker like Madrox.
Of course, as the kicker, Pietro would forcibly expose Luna to the Terrigen Mists years later. She survived, so I guess he had that going for her, but he lied baldly to cover his ass and wound up with his daughter hating his guts and his now ex-wife married to Ronan the Accuser and seemingly fairly happy. Ha, ha.