Was that a hiss?!

I think I heard Tiger hiss at Angel! We got them as litter mates when they were both about 8 weeks old. It's been a few months and Angel is usually the more dominant one. Well, I was in the kitchen, hearing Tiger play with one of his jingly balls and then a hiss! I look around and they're both staring at each other with their ears back! Of course the jingly ball is between Tiger's paws and then Angel starts backing up like with a "What in the world?!" kind of look.
Should I be worried? Angel always gets jealous when I start petting Tiger and starts a play fight with him. He's always gentle and just defends himself. Funny thing is she may be a bit older than him, but he's bigger than her!
I don't want this to get worse though! He's been carrying his toys to our bedroom lately which I've been finding cute to seeing them in his mouth but is he becoming protective over his toys? She plays with them too being that they're shared toys although she prefers the feather stick and laser pen.

Even the friendliest cats will hiss at each other once in a while. I wouldn't worry about it. Sounds like they're just having a little tiff over a toy.

I have three cats, and one of them can get his nose out of joint if one of the others just looks at him the wrong way. Hissing is very natural; they just need to work out their issues on their own. If it escalates, however, that could be more serious.

We have two kittens, that are a month apart in age. Mia is a hisser & growler, even when she plays with a toy alone sometimes.