Why Psyducks have Headaches
A scientific explanation for one of the most well known facts of Pokémon.
When you've watched Pokémon for awhile, several things become apparent: no Pokémon can say anything more than their own name (save for special exceptions, such as Meowth and a Gastly in the episode, The Ghost of Maiden's Peak), Ash is very gullible, and Psyduck is holding his head most of the time because he has a very bad headache.
The question is, why does Psyduck have such a powerful headache? One explanation is as follows:
All Psyducks are born with psychic abilities, one of which is telepathy. However, without proper training, they are unable to control these abilities. For the most part, this means they cannot use their abilities at all. However, they use the telepathy without even trying to. Unable to control it, they read the minds of all creatures near them, creating a mental jumble. It would seem like it had a screaming crowd in between its ears. Their inability to turn off this commotion, which they hear day and night unceasingly, gives them their trademark headache.
A related, well known fact is that when Psyduck is hit on the head enough, his psychic abilities kick in. One possibility is that, if a Psyduck's headache is based on too much psychic information, then, when noise or physical pain is added to it, it causes the rest of its psychic abilities to activate. Either by instinct, or through training (unknown due to the fact that it has not been shown if wild Psyducks can use their psychic abilities), the Psyduck is able to control their telepathy, sorting out which trains of thought they wish to hear and which to ignore. Most likely, a wild Psyduck is able to physically defend itself with its claws and weight, given enough trauma to boost their headache, and only trained Psyducks are able to use their psychic abilities in ways other than telepathic.
This theory would suggest that a Psyduck whose psychic abilities are active (shown by a blue glow to their eyes) is able to read the minds of both their trainer and their opponent. Not only would this make vocal commands unnecessary, but it would also mean that a Psyduck would be able to know what move an opponent was going to make as soon as their opponent did, and react accordingly, making it completely untouchable.
Inadequate proof is available, either to prove or disprove this theory. We can only study Pokémon every morning and afternoon, and follow what few clues it offers to this mysterious fact.
Here I'd like to thank my brother for giving me the basics for this concept. Before, I just figured Psyducks had headaches, period. Though that is another possibility…