Is a watercress poisonous or non-poisonous?

Absolutely. Non-venomous means exactly that... Species that don't employ venom to subdue their 'prey' usually employ the constriction method.

There is not easy way ! The best way is to research reptile species native to your country, then you'll recognise any you might encounter !

Presuming you are talking about Nelumbo species, then all parts are edible either raw or cooked. Although for any real nutrition, eat the roots after boiling them. There is no point in eating the...

Some do but they are mistaked as poisonous snakes and are killed like in florida....................... and non poisonous snakes eat the poisonous ones should be worshipped the have saved alot of...

No. Non-poisonous sea creatures greatly outnumber poisonous ones.