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heat engine
it utilizes temperature differential between ambient room temperature, and bird head which gets cooled through evaporation
>bird takes a big sip
>felt/flocked bird head gets soaked in water
>water evaporates and cools the liquid inside the head
>when liquid is cool enough, liquid travels back to bottom half
>bottom half has no cooling so the liquid heats back up again
>when liquid is hot enough, it travel to the top half
>this causes the bird to take another sip
