The first of those occurred in the third period, when Chicago forward Bryan Bickell made a rather poor decision with his left leg.
That's Blues forward Vladimir Sobotka at the receiving end of a knee-on-knee hit by Bickell. Sobotka wasn't injured after the play, but the hit will still likely be reviewed by the NHL Department of Player safety.
The aftereffects of the hit will haunt the Blackhawks for the rest of the series. While the Blues were on the power play, Brent Seabrook was ejected for a vicious hit on David Backes and could be suspended for awhile. Oh, and the Blues took the momentum and ran with it, tying the game with six seconds left.
That's why we keep our knees to ourselves, Bryan.