Why can't you watch your snakes eat inside their vivs? I watch all of mine eating.
If they really want to eat inside a hide, shouldn't you just let them do so?
There aren't any stones in the substrate I use (as for what happens in the wild, you know as well as I do that this can't be proven). All I will say is that snakes have been incredibly successful over millions of years, eating prey items in deserts, jungles, meadowland, even underwater. It's not common for them to choke to death on a bit of grass.
As for aspen - I think a digestive system that can dissolve fur and bone will make short work of a bit of aspen! Their guts can cope with rodent claws and teeth - or do you remove these before feeding as well?
Draco dormiens nunquam titillandus
“... there is no shame in not knowing. The problem arises when irrational thought and attendant behavior fill the vacuum left by ignorance.”