This is because, when she lies on her back during her fight with the hapless Midnight, Dave Cockrum shows it flattening out under the pull of gravity.
Compared to the other revelations in this tale, the fact that Mantis' breasts move might not seem a major plot point - or even two major plot points - and it isn't but it's always been one of my bugbears when a comic book artist shows human soft tissue being totally immune to the effects of external forces such as gravity and inertia, giving the impression that the characters are made from some form of living concrete. Frankly, looking at the way most super-heroines are routinely depicted, you do wonder how the undertakers are ever going to get the coffin lid shut.
But of course, while my focus might be on Mantis' anatomy, plotter Steve Englehart's attention is on an altogether different anatomy - that of the Vision.
Avengers still keep coming up against members of Kang's Legion of the Unliving. This time out, Mantis makes short work of Midnight, while Thor goes on a one-man avenge trip against Kang, after discovering Iron Man's seemingly dead body.
With Kang doing a runner after getting fed up of Thor hitting his force field, Immortus uses his own Magic Limbo Powers TM to restore everyone to perfect health, sends the component parts of the Legion of the Unliving back to where they came from and promises to reveal everything there is to know about the origins of the Vision and Mantis.
But of course this is the issue where we get the start of the whole process of Vision-origin-unveiling, as we're given the big reveal that the synthezoid is in fact the Original Human Torch.
We find this out when the Torch inspects the Vision's mortally wounded body and spots something that astonishes him.
Avengers #93, the nature of that discovery is never explained to us. Still, I do remember how important and gob-smacking this issue's revelation seemed when I first read this tale all those years ago, even if now I'm not sure it's the best way to handle it. I can't help feeling it would've been better to just give us a teaser that there was a big secret behind the Vision's creation and delay the full reveal until the the issue that specifically deals with the Vision's beginnings, rather than shoehorning it into a story about something else.
Something that does bother me in the issue is that people keep saying Iron Man's dead because he has no pulse and no heartbeat.
But how do they know?
For one thing he's wearing armour and, for another, no one who says it ever seems to actually make the effort to check or even get close enough to find out. It seems to me they're all a bit too quick to declare him gone, almost as though it's wishful thinking.
I don't know, you give them a mansion, give them a butler, and still they can't wait to get rid of you.