My friends talk about silly things and I feel like I am the stupid one.What should I do?

Hi!My problem is that my friends talk about things and they think they are interesting.They usually talk about birds and cats and they make some funny noises imitating squirrels and after that they start laughing and I personally don't find things like this very funny.And I have never noticed that before and I used to laugh too, but now I feel stupid 'cause I'm the only one who is not laughing.They say "Hey! whats the matter?Why are you so boring' and I just smile and move on.And others react like the things my friends say are really cool.So what should I do?I don't wanna talk about super serious things like politics but why not to talk about music and movies...I tried but the topic was changed to "lets make up lyrics"...the song was called: you killed my eyes...Help.I think that I should mention that I am 17.Thanks for your time!:)