"I know" and "six" or "You're" are the English equivalents of the Italian and Portuguese word sei. Context makes clear whether it is the first person singular present indicative in Portuguese (case 1) or the number "6" (example 2) or the second person informal singular present indicative (instance 3) in Italian. The pronunciation will be a very quick "SEH-ee" in Italian and Portuguese.
Chi sei? in Italian is "Who are you?" in English.
És bonita! in Portuguese is Sei bella! in Italian.
Sei bella! in Italian means "You're beautiful!" in English.
Sei bravo! in Italian means "You're good" in English.
"Six" in English is sei in Italian.
sei li?
Perché sei arrabbiato? in Italian means "Why are you angry?" in English.
Tigrotta sei! in Italian means "You're a little tiger!" in English.
"You are horny!" in English is Sei arrapato! in Italian.
"You are special!" in English is Sei speciale! in Italian.
"Are you safe?" in English is Sei salvo? in Italian.
"You're in charge!" in English is Sei in carica! or Sei responsabile per...! in Italian.