Why isn't my guinea pig oinking?

[Agent Abe Caprine]

Is it stupid?

 

[Caralho]

Autism most probably

 

[Just A Fat Round Bird]

They are learning their oinks from the parents and it probably has identified you as its parent stand in. So, all you have to do is show it how to oink, perhaps oinking at it for half an hour each day should do the trick.