How could Chihiro tell which pigs were her parents?

Question

In the early scene of Spirited Away, Chihiro's parents were turned into pigs.

I don't remember how she knew if the pigs were her parents or not.

How could she tell?

Answer 1

Because Haku told her, but also because she knew what was important.

When Chihiro is faced with the Yubaba's final challenge, she is told she gets one chance to find her parents. Haku has explained the rules of the challenge to her, but also told her that Yubaba doesn't want to let her go - and so presumably has told her that Yubaba is likely to cheat, and not include Chihiro's parents among the pigs she is told to pick from.

When Chihiro tells Yubaba that her parents aren't there, that's the correct answer. This shows that Yubaba did indeed cheat, but also it shows that Chihiro learnt what Yubaba didn't - when Zeniba took away Boh (the baby), Haku told Yubaba "You still haven’t noticed that something precious to you has been replaced." and her first reaction was to look at the pile of gold she had gotten from No Face, before realising that what she thought was Boh was a trick. In comparison, by the end of the film Chihiro has learnt how important her family is, and even in their transformations should would be able to recognise them amongst the other pigs if they were really there.