In Order of the Pheonix, Harry enters Snape's Worst Memory. The memory starts out in the Great Hall with students scattered about testing, but: why can't Harry find Snape at first?
QUOTE
Harry looked around carefully. Snape had to be here somewhere. This was his memory.
Notice the italics. When Harry finds himself in Dumbledore's memory in the Goblet of Fire, he lands right next to him, and can only hear what Dumbledore hears. Why doesn't Harry land right next to Snape, and why is he able to venture over to James' desk and see exactly what James has written, and hear exactly what James is saying? She describes Harry as moving almost dream-like over to James. As though he's being brought to James, because he is supposed to being paying attention to only what James is doing in this memory.
It's a memory, an emotional point in your life of some sort, not a snapshot in time. You can't wander around in a memory. Rowling writes:
QUOTE
...still buried in his examination questions; but this was Snape's memory, and Harry was sure that if Snape chose to wander off in a different direction once outside the grounds, he, Harry would not be able to follow James any farther.
Rowling constantly tries to make us remember the fact that this is Snape's memory, and she, of course, makes him follow the trio so we wouldn't suspect this could quite possibly be James' memory.
We see everything from James' point of view. His little fight with Lily, what he wrote on his examination papers, rumpling his hair all the time, his showing off for a 'gang of chattering girls', his Levicorpus spell on Snape, his playing with the golden snitch and Wormtail watching him in awe. If it were Snape's memory, wouldn't it have started when his little quarrel with the trio began? Why would it have started at the end of the exams? Nothing of any consequence or significance happened at that particular time, surely nothing that Snape would want to stow a memory away for. He had his nose buried in papers almost the whole memory. And if it were Snape's memory, we'd be reading about the bushes he's sitting behind, or what he had written on his precious papers. She makes it very clear, many times, that Snape isn't paying attention to anything else until Sirius starts taunting him. Why then, do we know every word of their conversation? Why do we know almost every emotion James experiences, and move he makes?
Why would Snape have James' memory? Why did he pull Harry out at a certain time? Perhaps something was about to happen that would give something significant away about why there was so much tension between Snape, Lily and James? Maybe there's more to their relationship that we don't understand. Maybe there's more to James that we don't quite understand.
<3. Hopefully that made sense.