Parseltongue

Parseltongue supposedly the language of snakes, and a Parselmouth the one who speaks it. But do snakes in fact have a language? I would argue that a more accurate definition is that the Parselmouth exudes a magic that imbues in localised snakes extra abilities including

• the ability to understand Parseltongue
• extended intellect - possibly a variable amount of extended intellect based on the Parselmouth’s level of focus on the snake in question? Cannon allows for different interpretations.¹
  • The basilisk appears to have very rudimentary levels of sentience, expressing very animalistic desires only.
  • The boa constrictor appears to have an understanding of more abstract concepts like being annoyed by visitors, and home.
• the ability to blink - snakes do not have eyelids to do so in nature.
• an understanding not only of verbal language, but of human style body language, the boa constrictor uses a human style head nod.

The two things of note that lead me down this interpretation are

1. the fact that the boa constrictor has more than just a language ability, it uses human winks and nods as well in the presence of a Parselmouth.
2. the fact that the basilisk appears to express itself much more the way we expect an animal to - raw barely structured emotion.

This corresponds to the way the Parselmouths in question would have formed their expectations: Harry wanted a conversation and so his magic imbued its target with the ability to respond at a level able to converse. Riddle saw the basilisk only as an animal and a servant, never as a someone. Thus the basilisk was in fact less capable.

While I recognise this is a massive amount of speculation, it fits the facts, and preserves the line between sentience and sapience.

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1. I am purposefully not considering Nagini, the [Fantastic Beasts] back story introduces too much complexity that Mrs. Rowling may or may not have considered when authoring the relevant sections of books 5, 6 and 7.↩︎