I love the psychological answer of Klaws.
To add a bit more poker content, tensions builts up when there is a confrontation of good hands (like AA, KK, or AKs) and bad hands like (46o, o means off-suit) on a dynamical flop where every one has caught something.
Keeping it simple with two players, both AsKs and 4h6d are happy on a 3s4d6s flop.
The preflop action could be AKs opening and 46o 3-betting as a bluff and then AKs just trap-calling instead of 4-betting. Another possibility to get a huge pot is 46o opening, AKs 3-betting, 46o 4-betting as a bluff and now AKs has not a real incentive to 5-bet as it is turning its hand into a bluff and should fold if stacks are huge and the opponent 6-bets all-in, so he may just call with a huge pot developping.
Now the 46o player can put a lot of pression on AKs because he was the last to raise and he is now virtually in position.
On the flop which has two spades, the 46o player should continuation bet to protect his vulnerable hand with two low pairs on a wet board, but he can also decide to trap and hide the force of his hand by just checking, which builds more tension.
On 3s4d6s, the AsKs only has a flush draw (8 outs) plus two over cards with 6 more outs (3 Kings and 3 Aces which would give him a pair of Aces or Kings) with a total of 14 outs which usually makes him a favorite but with so much preflop action indicating a possible monster for his opponent, and being out of position, he should be carefull and bet the flop about one third pot bet size.
The 46o player can then raise him as he would do with AA or KK without the As or Ks which the omnicient spectator knows he can't have as it is in the hand of the AKss player.
On this raise, the AKs player can just call and wait to find a spade on the turn or river to put more money in the pot.
An innocent 2h turn could slow down the action as the 46o player should not feel threatened by this card not being a spade and as a river 5 would give them a straight.
So if they go check/check and try to see any tell of fear or weakness in each other composure, you can elaborate on that.
The river is of course the 4s which gives the highest flush to AKs player and a full house (boat) to the 46o player and depending on the level of the players, a serie a check, bet, raise, re-raise could end up on a rere-raise or a fold from the AKs player. The fold being even more dramatic because of the uncertainty for the folding player, not being sure even if he decided on the right decision that he has not being bluffed.
Another interesting river card would be the Ace of heart with reverse pressure applied by the AKs player who could potentially represent a set of Aces and try to make the 46o double pair player fold...
A river J, where the AKs player knows he has lost and his only hope to make the other player fold and win this huge pot, sensing false weakness by the turn check or imagining that the other player having KK could fold to an all-in raise representing he having JJ for a set of Jacks, the action would be:
46o player checks again to trap, AKs player bets, 46o player raise with his invisible two pairs, AKs player raises, 46o player is a bit concerned not being sure his two low pairs are any good and should just call but decides to bully by re-raising. AKs player knows his only chance is by going all-in, having more JJ than his opponent, so he does. And 46o player has to fold the better hand !
Of course you need monster stacks and ego for this to happen.