All animals are like humans,they all have their differnt mood swings & quirks & some cats can be very loving & with no reason turn the other way so ragdoll is most probaly one of them,the fact the two of them are playing is great news,more of a worry if it is real nasty attack on the newbie than hissing,my household of furries has only just settled down into only the occasional hiss between them four years after the new babes were introduced & we are now going to upset the apple cart by bringing in another.I always used to have water spray bottles about everywhere {down to one in case now but not been used for ages} & if the hissing got too aggressive rather than saying just no I would squirt & say no the first time & if I had to use it again wouldn't say anything so in the end if they started getting OTT with one another just picking up the bottle would make them part & walk away from each other.They are all the best of friends now but you still get the odd hiss but who came blame them when that other little upstart furry comes along & dares pinch your favourite toy. It sounds as if the two in your household will become great mates & playtime with them both & a feather tickler can be a great leveler....x