You can technically handle poison dart frogs all you like and be perfectly fine. It's not until the poison touches a mucous membrane or an open cut that it actually takes effect. Dart frog deadliness also varies from species to species.
When Linda and Tulio notice that their canoe is coming towards a waterfall, they act frightened and start back-paddling like crazy, when all they had to do was climb out of their canoe before it reached the waterfall.