“One excerpt shows a group of dolphins nudging and chewing on a pufferfish, causing the fish to release its defensive toxins. They then pass the fish around, take in the toxins and appear to go into a trance-like state.” (http://uk.whales.org/news/2014/01/documentary-reveals-more-unusual-side-to-dolphin-recreation)

Taking enough toxin for recreation without harming yourself shows more intelligence than certain other species.