not entirely sure, but maybe some sort of gravity was involved.

The idea is that a mammalian body (or Groot, since he's also affected) can't handle that many jumps. Jumping through the network like that screws with your body

Its odd that Yondu says "mammalian body". Does this mean that this affects mammal-like creatures (including humanoid ones)? Or is that suggesting Yondu, Groot and Rocket are actually mammals? I mean... one could argue that humanoid alien races across the universe might have a common ancestor with humans on Earth (through Celestial shenanigans, or something) and I suspect Rocket has actual Earth raccoon DNA as well. Also begs the question if Howard the Duck would have any problems with these jumps.

Howard the Duck is invincible. Nothing would effect him :p

^you heard it people.

Well, Howard the Duck is a duck, not a mammal. However, there are of course problems with Groot being a mammal too, since he's definitively a plant.

He's not a plant. He's a Flora colossus. Big difference.

Yeah, but that's still part of the plant kingdom, no? He appears to be structurally no different than one of Earth's trees

He could be a "mammalian" equivalent to whatever native biota exists in Groot's planet. I mean... one could see his world being completely dominated by plant-like life... and some plant-like organisms evolve to more animal-like metabolisms, and Groot has evolved a very humanoid (therefore mammalian) like bauplan.

To be fair, I believe the term mammalian would have applied to their brains, as mammal brains are the largest among all animals on Earth, and are the ones that belong to the most intelligent species on Earth. Translating that to alien creatures, I suspect he meant anyone who had a mammalian like brain anatomy. This might not add up with Howard the Duck not being a mammal. We know birds can be intelligent, but his way of acting is very human-like, so one would assume he would have a mammalian like brain. Unless Howard the Duck is a platypus or something XD.

That's very possible