Popp thinks that if one of those crops up, he might develop a severe phobia of snakes on the spot.

"That's... a lot bigger than my dragon form. A little bigger than the biggest dragon I've seen, even!"

Uuuuugh but he's being a supportive friend. He flits up into the trees, hoping to find a snake on a more modest, non-tree sized scale. Heh, heh. Scale.

"...Hey, if something like that shows up, can you fight it?"

Running is theoretically always on the table because of Popp's skillset, and this is a situation in which he has the luxury of bailing. They're just here to explore. The only thing at stake here is that Sephiroth will think that he is a weenie, which he is weighing pretty heavily, as a motivation.