Netherthorns spawn at any light level in the Nether, on top of netherack and soul sand. They mostly spawn in a group of 2 to 10 and can be placed on Netherack and Soul sand by the player.
Netherthorn looks similar to a dead bush, but are burnt orange in color.
Netherthorns are considered a dangerous block to mobs and players. If Netherthorn is stepped on they give the mob or player one (half a heart) damage per second, similar to cactus. Also like cactus, any items that come in contact with Netherthorn will despawn. Like tall grass and dead bushes, they can be broken by the player instantly but can't be placed in flower pots.
Interaction with Mob AI
Mobs do not avoid Netherthorns, making them useful for traps or just weakening mobs coming your way. The downside is the player may lose any mob drops due to the Netherthorns despawning them.
A good way to obtain Netherthorns is breaking the Netherthorn using Shears or the block below it.
In traps for mobs and players, such as a two block deep pit filled with Netherthorns. Also as decoration or a compact trash can were players can dump in items to destroy.