Both boobs are concerned one after the other: regarding my 3rd wife, two people together (as well male as female) synchroneously slapped each udder randomly, therefore they spinned round for each slap in the same direction... Moreover being naturist my wife never weared useless bra or other sustaining device, she was BRA-LESS in every circumstances, i.e. jumping or playing volleyball, kind of sports extremely stressing for any female breast, especially for the well endowed females. My wife had only normal (neither too small nor too big) superb endurant nipples. I loved them!
You would like to get your udders hard slapped like the ones of my lovely 3rd wife who furthermore always enjoyed such an excellent treatment without neither shame nor damage for her nipples!