Something Weird

I discover something weird today. Maybe this is something usual for somebody else but this is the 1st time i saw it. I go back to my sister's house yesterday and today i helped my elder sister to look after her 3 years old daughter. This afternoon, i've scaned some old pictures into my laptop. I then accompany my niece to look at those picture and suddenly she cried. She cry, cry, cry, n cry..i wonder why she is crying. I just looked then i noticed that she'll start to cry when she sees her mother's pictures. Everytime when she sees a picture which have her mother in it, she start to cry louder n louder. she'll never stop. OMG!!! But eventualy, she stop at last when her mother came back from work. And just now, when her father ask her to see some picture again, she cried again..I'm confuse what make her act like that. This is something i'd want to know more..