Learn Finnish: Miksi sinä puhut käärmeille? - Why do you talk to the snakes?

The base word is käärme. For Finnish words ending in -e, the stem usually has a double vowel, making it käärmee-. To make it plural, the plural marker -i- replaces the final vowel of the stem, giving us käärmei-. Finally, we add the allative ending -lle to get käärmeille (to the snakes).

Why do we use the allative case (-lle) with this verb?

The verb puhua (to speak/talk) requires the allative case (-lle) when you are talking to someone. You can think of it literally as directing your words "onto" the listener.

Does käärmeille mean "to snakes" in general, or "to the snakes"?

It can be both! Finnish does not have articles like "a" or "the". Depending entirely on the context, this sentence could mean "Why do you talk to snakes?" (a general habit) or "Why do you talk to the snakes?" (referring to specific snakes right in front of you).

Is it okay to drop the word sinä from this sentence?

Yes, absolutely. You can just ask Miksi puhut käärmeille? Because the verb puhut ends in -t, it already clearly means "you talk". Including sinä just puts a little extra emphasis on the "you".