Its all got to do with the right environment for the sperm. Apparently both commercial lubes and saliva are not great for the little swimmers, so they suggest you use either real eggwhite if you are low on EWCM or Preseed, a more spern-friendly lube. I agree with the others tho, re where the sperm gets "deposited" and where the saliva would be. I can't see that the two would be in any contact at all (unless he has a really, really long tongue... :smt016 )