Haunting positions #2

Another positions that keeps coming back from subconscious is this mate in one with white to move. The reason I guess it is that it is a bit against natural instinct. It is nice that I am one to deliver. This is from 5 minute blitz game in FICS. I am not sure how difficult it is. I had 3:12 and my opponent 2:56. For me it took 5 seconds to see it.