What happens if somebody accidentally splatters a little spit on you when you are talking. could somebody contract aids from this?

Highly unlikely.: While it is theoretically possible for a drop of spit / saliva to carry hiv, it would be highly unlikely (virtually impossible) unless the spit contained blood or pus that was infected and the person upon whom the spit landed had an open sore into which the spit fell. With 'regular' spit and 'intact' skin the likelihood of transmitting HIV is likely too small to measure accurately.