The Na'vi seem very in-touch with scents, so he could probably smell it on both of them, especially with them together.
Neytiri has telepathy with neytiri duh people these days
Jakesully says "don't do this brother. Tsu'Tey threatens him first. Neytiri answers but it is not translated. Can anyone translated what was said?
1. Jake Sully and Neytiri said nothing about their 'marriage' to Tsu'Tey. Tsu'Tey said about it before Neytiri's confession. How did he get to know about it? Had he a spy? I think he did not need a spy at all. Naytiri and Jake Sully just did not go back to sleep to the Home-Tree that night. It was enough to Tsu'Tey to understand what was going on.
2. At the end of the dialogue quoted above Neytiri answered rut'e (ɾu.‟t‟ɛ), what means 'please' in Na'vi language. She tried to stop the fight between Jake Sully and Tsu'Tey.
the complete Na'vi language site - http://www.learnnavi.org
EDIT: I belive Tsu'tey knew Neytiri and Jake mated because of the way Neytiri was dressed. It possibly could have been cerimonial for mating for life. It was the only time we saw Neytiri with her hair down. 3. tsu'tey might have noticed that jake and neytiri were bonding and becoming closer and closer together.
4.He saw them leave the tree of souls together in the morning. This was the place to mate before Eywah for life. P.S loved the collectors cut, Neyteris' sister was killed in the school,Buffalo hunt was awesome, Bulldozer war, etc, etc. The movie makes alot more sense with the sixteen minutes put back in.
tsu'tey knew the tradition, when jake was officailly part of the clan, jake could mate any woman in hometree