Sometimes it becomes necessary to interrupt a woman mid-sentence; for some its a never ending sentence. 
But seriously, I do it because if I don't put my two cents in at the time, I will forget what it was I was trying to say.
I interrupt both sexes, (I guess I will have to change that to multiple sexes), though I can't swear that it is on an equal basis. 
Just one more problem with old age.  
Look a squirrel!
What was I saying?