wˌɛn ɐ lˈɔŋfɪn ˈiːl bˈɛndz ɪts lˈuːs skˈɪn ɹˈɪŋkəlz dɪstˈɪŋktɪvli ɪnsˈaɪd ˈiːtʃ bˈɛnd, wˌɛɹ ɐ ʃˈɔːɹtfɪn ˈiːlz skˈɪn ɪz smˈuːð.
When a longfin eel bends its loose skin wrinkles distinctively inside each bend, where a shortfin eel's skin is smooth.