Hearthstone turns shouldn't last more than a few seconds. And they rarely do, but there are always exceptions. Using Dreadsteed cards with Knife Jugglers is one of them, and this particular moment almost created a never-ending turn.
Dreadsteed is a new card, added in The Grand Tournament expansion. It has only one HP, but it will respawn on death. The other card, Knife Juggler, deals 1 damage to a random enemy automatically after we summon a minion. It's not difficult to see that a bunch of these cards on both sides can lead to an infinite loop of 1 HP damages and constant summons.
And that's exactly what happens in The Optimistic Brit's replay, with both players slowly losing their health while the battle between the Dreadsteeds and Knife Jugglers just won't stop for 16 minutes.