It already starts with the covering act. Only the dog-like animals know the phenomenon of »hanging« during the act of reproduction. But until now, nobody was able to find a satisfiying explication for that pecularity. The most plausive explication was the one that says that it's this way that a returning of the sperms can be avoided for a longer time. But why can't we find this appearance with other animal species? Meanwhile the behavioural research discovered similarities with the behaviours of other animal species...

Read more about that in the YTJ 39.