I was tempted to just post this with no explanation whatsoever, but in the name of education I'll give a few words. If you haven't watched the above action-packed penis footage, you probably should before you read on any further.
Most birds don't have penises. But ducks do. They have huge penises, absolutely enormous. Not only are they freakishly well-hung, but they are corkscrew shaped. So ducks have gigantic, horribly deformed dongs.
Male ducks get really, really horny during the breeding season. They are notorious rapists in fact. Female ducks do not really benefit from being raped by a males they do not want to mate with (shocking, I know), so they have evolved crazy vaginas that corkscrew the opposite direction of the way duck weiners go. They even have dead ends in there! And if you are wondering, when females willingly copulate their vagina maze relaxes and straightens out.
Did you ever think you would read the phrase "vagina maze" on a bird blog? Maybe "vagina maize" would be weirder.
But I digress. One of the males' evolutionary tricks to combat the twisted and labyrinthesque duck vagina is what you see above...the exploding penis. With such force propelling their duck dicks forward (and some luck), their misaligned penises can push their way up into duck vaginas, whether the female likes it or not.
It's strange to think that forced copulation is ostensibly such a powerful force in duck evolution. This wonderful penis video was inspired by my friend Socrates, for reasons best left unexplained.