
Ooooh.... *dons tin hat*...
I actually agree with you both but Vera, you are not actually helping the OP whose concept of aggression is not the same as yours.
Aggression, ie, growling, snarling, biting, is a TOOL in a dogs toolkit - its there for many of the same reasons we can use it, and it comes out to play to deal with immediate situations, usually caused by fear - fear of being hurt, fear of losing something valuable, fear of the unknown etc..
Aggression IS NORMAL. ALL dogs have the ability to use aggression just like all people, all adults, all toddlers, all OAPs...
The differences are that a toddler will shout NO! and kick and thump and bite, the OAP will belt you with a walking stick, the drunken adult in the street will hit you wtih a bottle.... but its all a normal thing we all have the ability to use.
Like the toddler, the puppy doesnt have the life experience to know when a simple 'i dont like that' would suffice, in fact he doesnt know how to SAY 'i dont like that' and its up to the puppy owner to teach it.
Some puppies use aggressive behaviour far more readily than others - this does absolutely NOT mean they are going to grow up evil nasty vicious adults - the ability to be aggressive, and the immature, juvenile animal useing aggression when it has no other alternative does NOT mean a dodgy evil nasty adult, not at all!
However, ifyou dive in headfirst and do what Whistler posted above, take things off the puppy, shout NO when it growls and thus teach it that when hes fearful he may lose something, he is right and he WILL lose things, you are liable to teach a puppy to use aggression! So.... dont do that.
Prevent puppy from feeling the need to use aggression - dont take things that are his, if he growls to tell you something is scary/painful/unpleasant then dont go and stroke him or faff with him further. If you are worried, leave the 'scene' and think about what to do - reacting in anger to a puppys behaviour is never sensible!
Understand that whats in his mouth is his - you can and should teach him to give you things he has on command but this is achieved by teaching him that you have something better, never by snatching or grabbing, at best this teaches him to run away with things hes found and at worst he will learn to use his teeth to defend his 'property' (and being a dog hes got naf all idea that you paid for the mobile phone and its worth £200 so complaining that its not acceptable for a dog to steal your stuff is pointless and a waste of time. Accept these things will happen, stay tidy and put things away, and teach your dog that YOU have wonderful things and are worth listening to, not to be feared!).
Puppies teeth are really sharp for a good reason - they are small, clumsy, move relatively slowly compared to adult dogs and this and their loud yelps/growls (which they will have been practicing since they were a few weeks old) is ALL the have to defend themselves and their stuff.
When you have a toddler to consider, play biting, over enthusiastic playbiting, a pup more willing than others to use his teeth and mean it (perhaps one bullied by his littermates, or perhaps one from a smaller litter who WAS the bully!), its serious no matter what the intent is.
You cannot however expect the puppy to understand, any more than you can expect the child to - so keep them seperate, dont let either one annoy the other, puppy toys are not kids toys, kids toys are not puppies toys and its your job to make sure that that is made clear (by putting away the kids toys, by teaching the child not to take or mess with the puppies toys).
If you teach your pup bite inhibition and never give him any need to defend himself or his stuff, he will not grow up a problem adult (unless there is some underlying medical problem, which is highly unlikely). It sounds like the incident you describe in your first post was a case of an over tired wound up puppy who doesnt know how he could have politely ended the game - although perhaps he tried we dont know, did he attempt to take his toy off by himself, put a paw over it, lie on it etc before he snarled and bit? Its quite clear that once that far wound up, you going to stroke him was viewed as a threat and that is why he bit you.
Look out for signs that he wants to stop playing with you and take his toy off by himself - stop playing BEFORE that happens. Get hold of books about dog body language (i like Turid Rugaas but there are others) so you can recognise the signs and respond appropriately.