Board Thread:Theories and Speculation/@comment-1005186-20160610173059/@comment-5407586-20160611070048

In Sage Mode Naruto's sensing abilities are rather high, but not quite at Karin's level; if Karin can't sense Zetsu when it's using Mayfly, then Naruto can't do it as well. With Kurama's chakra he senses negative emotions, so he can detect Zetsu quite easily.