What's he got in his pocketses...er, offices?

[snapeschambers]

No: HPFGUIDX 71279

Okay, I've looked on several Potter sites out there and haven't 
found any discussion of something that's been bothering me...

In GoF, Ch. 25: The Egg and the Eye, Snape appears (in a gray 
nightshirt :D) and talks to Filch about someone breaking into his 
office. But when Moody arrives, Snape tries to prevent Filch from 
telling Moody:

"...Professor Snape discovered that someone had broken into his off-"
"Shut up!" Snape hissed to Filch.

However, Moody has heard Filch, and asks Snape about it:

"Someone broke into your office?"
"It is unimportant," said Snape coldly.

He's actually very upset about it (a "vein flickers horribly on 
Snape's greasy temple") and Moody asks if he's hiding something.

As far as I have been able to tell, nothing comes of this. We don't 
find out what Snape is hiding, or if he is, indeed, hiding anything. 
I have a few guesses as to what he might be hiding:

1) Death Eater costume...he's going to need it if he turns spy 
again, and it would be rather hard to explain.
2) Evidence that he is a double agent? Perhaps some of Tom 
Riddle's "old school things", which he's hiding for Malfoy?
3) Mementos of his past that would be embarassing if revealed? 
Tattered pictures of Lily, perhaps? His old teddy bear?

This is really bugging me, because it feels like I've either missed 
something obvious, or a major clue has been dropped and then never 
mentioned again. Help!

--SC