http://www.accesstoinsight.org/tipitaka ... .than.html
" And what are the fermentations to be abandoned by avoiding? There is the case where a monk, reflecting appropriately, avoids a wild elephant, a wild horse, a wild bull, a wild dog, a snake, a stump..."
Might it hide a snake? Is it because it's an unsuitable seat? If so, why is it unsuitable? What seats are unsuitable?