new visitors to my tank

I have been stocking up my new tank slowly over the last few weeks and have noticed that, in the process of buying new fish and plants, I have introduced a couple of snails to the tank. They are tiny and have little shells with a sort of curly conical shell. My three Black Marbled Angels seem to try and eat them but spit them out as soon as they realise they have shells.

Is this normal and will they have any detrimental effects on my fish??

Thanks

Stu

cool and thanks for that - I had a look through the posts but I am still struggling to see why people HATE snails - do they actually do any harm to the tank or the fish??