Threats are things that will try to kill you
Hunger and Thirst
These two threats are very easy to come across. They can be stopped though just have some cooked mackeral, cooked potato or any thing else cooked as it will replenish both hunger and thirst
The shark will cricle around your raft. After a while it will come and destroy your raft. If you spear it in time that peice of foundation will be damaged and the only way to repair it is with the building hammer. You can kill the shark and get its meat but it will respawn instintaniously.