bichirs always seem fine on sand until they swallow a stone and cannot pass it/regurgitate. When feeding they use a vaccume like gulp that often includes gravel along with their food. this can, and sometimes does, lead to death. i had a foot long beutikoferi swallow a pebble almost an inch long and it was in his system for almost a week, luckely he spat it back up and is fine. better safe then sorry.