simple crash log when practice with the swords.

java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) at java.util.ArrayList$Itr.next(ArrayList.java:851) at com.google.common.collect.Iterators$3.next(Iterators.java:163) at net.minecraft.world.chunk.Chunk.func_177414_a(Chunk.java:882) at net.minecraft.world.World.func_175674_a(World.java:3012) at mods.flammpfeil.slashblade.core.CoreProxyClient.getMouseOver(CoreProxyClient.java:503) at mods.flammpfeil.slashblade.item.ItemSlashBlade.onEntitySwing(ItemSlashBlade.java:2546) at net.minecraft.entity.EntityLivingBase.func_184609_a(EntityLivingBase.java:1350) at net.minecraft.entity.player.EntityPlayerMP.func_184609_a(EntityPlayerMP.java:1243) at mods.flammpfeil.slashblade.item.ItemSlashBlade.doSwingItem(ItemSlashBlade.java:2834) at mods.flammpfeil.slashblade.item.ItemSlashBlade.func_77663_a(ItemSlashBlade.java:1977) at net.minecraft.item.ItemStack.func_77945_a(ItemStack.java:437) at net.minecraft.entity.player.InventoryPlayer.func_70429_k(InventoryPlayer.java:344) at net.minecraft.entity.player.EntityPlayer.func_70636_d(EntityPlayer.java:510) at net.minecraft.entity.EntityLivingBase.func_70071_h_(EntityLivingBase.java:2020) at net.minecraft.entity.player.EntityPlayer.func_70071_h_(EntityPlayer.java:233) at net.minecraft.entity.player.EntityPlayerMP.func_71127_g(EntityPlayerMP.java:303) at net.minecraft.network.NetHandlerPlayServer.func_73660_a(NetHandlerPlayServer.java:162) at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher$1.func_73660_a(NetworkDispatcher.java:213) at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:287) at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:180) at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:732) at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:613) at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:240) at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:471) at java.lang.Thread.run(Thread.java:745)

Crash Log

It is difficult to fix.
"reach strech" function omitted.
commit: 39a3db2