It had been interesting times recently for one Erin Harper, fluctuating wildly between terrible and boring. The terrible things that had happened prompted him into states of mind he didn't much like, and the boring ones had given him plenty of time to be in them. It was liable to drive him mad if he didn't find something to distract himself with, and thus he was even now kneeling behind the wall of the 5th story staircase, in juuust the right position to peer out intently at the all of the stairs below.
 
He'd rigged up a slipping charm, standard issue and right easy to anticipate, on the second step of the first stairwell. Simple as it was, it'd already caught a dozen people in the past 15 minutes; it was, after all, a crowded staircase. The second one had a sticking charm, designed for those who were wary after the first. One deliberate footstep, and they were caught like flies. After the second one he'd had to get a little more creative; he'd cast an illusion on the third to make it invisible. Charms came easier to Erin than transfiguration, and he'd been practicing this spell for a week besides; so what if the stairs constantly flickered into sight and out? It was close enough, and probably more confusing that way. He was okay with it.
 
Then there was the next staircase. He'd found the spell mentioned in a memoir of the Weasley inventors' time at Hogwarts, something they'd performed during Umbridge's reign. There'd been no discription, thought after some time with a dictionary Erin had been able to determine part of it was the conjugation of "to spin"; the other word had something to do with ducks. It hadn't looked too dangerous, so he'd tried it on the fourth one. He didn't know what it did yet, but he was eager to find out. (Deceptively easy to cast - but he trusted the Weasleys when it came to pranking.)  And the fifth staircase had another sticking charm on it, though this was was a little more advanced; he'd need the extra getaway time should anybody spot his blonde head watching.
 
So far no one had. Erin, who had afternoon classes right now like everybody else, was almost disappointed.

Afternoons free were the prerogative of the first year.  While other years were toiling away at their afternoon classes, Mairead was off trolling the corridors for something to occupy her mind.  She could be studying.  And, perhaps, she should be.  But, of course, she wasn't. 

Her flute case tucked under her arm, the first year skipped onto the seventh floor stairwell and started to make her way down the moving staircases.  She had no specific goal in mind.  With her flute, she could end up anywhere and find a way to entertain herself even if nothing better crossed her path.  Halfway down the stairs, though, she spotted a worthwhile distraction.  She paused long enough to slip her shoes off her feet before padding quietly, barefoot, down another flight of stairs.  She plopped herself down on a step just a flight above the older boy and peered down at him, watching. 

It wasn't clear, at first, what the boy was doing.  He seemed to be watching something further down the staircase but, unlike Mairead, he had no obvious quarry.  That was until a foot slipped out from under a tall Hufflepuff that was climbing the stairs, sending him thudding down in a painful looking split. 

"Yer in me way!" The young Gryffindor hissed at the Slytherin as another Hufflepuff started down the stairs to help the one that had slipped.  From a distance, it didn't appear like the would-be hero was aware of the hazard.  She waved her hand through the banister at the Slytherin.  "Go n-ithe na péisteoga thú," she muttered.  "Move!"

Erin's head turned slowly, eyes wide and wary like the owl he so resembled. But when he spotted the hisser herself - toothpick arm through the balcony, snubby childlike nose, just a first year - he relaxed, and aimed a scowl up at the little witch.

"What the hell are you on about?" he demanded, loud enough to reach her waiting ears but not so loud as to drift below them, where now both Hufflepuffs were waffling about where they'd fallen on the first staircase. "You move if you can't see." Bloody children. He didn't know what she had muttered, but it sounded nasty. If she kept up at it he might have to involve his small-but-useful mental dictionary of Welsh terms to respond (over half of which were conveniently curses or other situation-appropriate words).