not sure how accurate this is but i heard there's bacteria on the anemone's tentacles that they ingest or they ingest the stinging cells and use those cells in it's slime coat to avoid stings by the anemone. from what i understand most clowns being hosted by anemones do this. my true percs did it when they were hosted by my condylactis nem but they dont do it to the frogspawn they now live in
ive seen my Maroon pair "love" my nems so much that the fluttering of thier tails twists single tentacles of my rbta around till it falls off, then my female maroon will eat it if the male doesn't clear it fast enough.
Biting is one way clowns acclimate themselves to the nems sting. They usually start by doing this and then going in and out head first. After that the drive bys start and then eventually all the way in.