Subject: Why do shadows seem to merge?

I am standing outside on a bright day with the sun at my back. I raise 
my right hand and move it slowly towards my head. When my hand is 
about an inch away from my head the shadow of each appears to form a 
lump facing the other shadow. If I bring my hand slightly closer to my 
head the two shadows seem to merge. Actually, my hand and my head are 
still not touching. What is going on?

Re: Why do shadows seem to merge?