cav·i·ty /kavitē/ - noun - an empty space within a solid object, in particular the human body.
mid 16th cent.: from French cavité or late Latin cavitas, from Latin cavus 'hollow.'
...
Dean didn't know it, but Sam completely avoided sweets after Gabriel died.
It wasn't his fault - a brotherly codependency could only go so far in such matters. He noticed Sam falling silent or staring off into the distance more often, but it wasn't something that became more frequent - it worried him, yeah, but it became clear he wasn't losing Sam to whatever that was, and so he left well alone.
He wasn't going to be a complete hypocrite about it. It's not like he was the poster boy for sharing feelings or bonding or whatever. Besides, it wasn't as if they had any specific reasons not to be depressed at any given point in time. Things were technically getting worse, what with all the natural disasters and demons and angels and crap.
And if Sam got quiet or pensive sometimes, in the sort of way one does when thinking of the past, Dean wasn't going to mess with him, and he wasn't going to pry. Sam kept those things close.
It could be anyone's death grabbing at his thoughts; it could be any of the shit they went through on a daily basis.
The Apocalypse, the angels trying to do who knows what to them (besides God, who was MIA as far as anyone knew), the death, ACTUAL Death, the horsemen in general, demons, monsters, Lucifer, that kid they watched have his eyes torn out an hour ago.
It could be anything.
Anything could be making him contemplative. If he chose the grim reality of this thoughts to cold, hard liquor, Dean wouldn't interfere just because he chose the latter. He didn't ignore it, of course, just let it be.
Besides, it wasn't as if Sam ever advocated a sweet tooth - he was practically a rabbit if you looked at what he ordered when they went out to eat. (The hell would someone order a plate of only alfalfa sprouts for? Seriously.) It made Dean a little queasy to think it, but the closest thing to red meat Sam had ever consumed regularly was demon blood.
And that was off the menu, now.
Anyways, Sam stopped eating sweets. It only took Dean so long because he doesn't generally share his pie.
So when he does offer it, Sam literally isn't supposed to say no.