Another difference between item and regular projectile interactions.

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If an item does something that would normally incur hitlag, like hitting a shield or hurtbox, or clanking and not outprioritizing, (and it isn't destroyed, obviously), it enters hitlag. If a projectile hits any of those things (and isn't destroyed, obviously) it doesn't enter hitlag, and continues through its animation with no changes. If anything reflectable is reflected in any way, it doesn't go through hitlag (at least as a result of the reflection), but non-powershield shield reflections still put the shielder through hitlag, don't transfer projectile ownership, and don't count as a collision for the projectile that hit it (so it can hit them again, in theory at least). Hitting a counter (like Marth's) to activate it does make the projectile go through hitlag, not the hitlag based on how much damage it would do if it hit something.

Sheik's Vanish hitbox acts more like a non-item projectile's here, as interactions don't change it's duration. Spacie side-special will not only last longer, but when it exits hitlag, it will greatly stretch the size of the hitbox on subsequent frames to cover the are it would have normally to the point where it's supposed to be covering if it didn't hit anything.

Examples of non-item projectiles that don't get destroyed by a few of these interactions: Ice Climber's Blizzard (does not clank), Ness's PK Flash (destroyed by Shields, does not clank), Bowser's Fire Breath (does not clank), Zelda's Din's Fire (destroyed by Shields), Blastoise Hydropump (Pokéball, non-reflectable)

Items: Any swingable item, Hammer Head, Mr. Saturn, Turnips, Shells, Flippers