Great Riddle! Kind of Hard Though,?

[Nick-Nack]

Okay, pretend there are 3 pens. One is yellow, one is blue and one is purple. The yellow one killed the blue pen and then she killed the purple pen. Both murders were accidents. The blue and purple pens are sisters. What movie is it?

 

[elitesouthwest]

Knocked Up

 

[CubeScience]

A Fish called Wanda