Where did he go?

[potioncat]

No: HPFGUIDX 96019

Something odd happens in OoP, "Seen and Unforeseen" pp593--598. This 
is the big scene between Umbridge and Trelawney in the entrance hall. 
Harry is taking occlumency with Snape when they're interrupted by 
screaming. Here is a quote and a brief review of the event:
 
"Snape strode to his office door, his wand still held at the ready, 
and swept out of sight.  Harry hesitated for a moment, then followed."

Upstairs Harry sees a large group of students watching Umbridge and 
Trelawney argue.  McGonagall is comforting Trelawney when Dumbledore 
comes in from the grounds and confronts Umbridge.  McGonagall, Sprout 
and Flitwick help Trelawney go back to her rooms.

What happened to Snape?  If we hadn't been told that he went to 
investigate, his absence wouldn't seem so strange.
Potioncat