pkpk was crying last night and now her eyes are swelled up.  Tears are strange; you cry when you're happy and when you're sad.  This discussion of tears reveals a terrifying plot!
Okay then, why not make happy 
and sad into one feeling?
Entonces, ¿por qué no hacer un sentimiento
de la felicidad y la tristeza?
¿Por qué no unimos la felicidad y la tristeza en un mismo sentimiento?
Então, por que não fazem a felicidade
 e a tristeza serem o mesmo sentimento?