--lua

local world = match(pl, arg)
if getn(world)>1 then
  send(pl, "You can only knock one thing at once.")
  return
end

local obj = world[1]

if !obj then 
  send(pl, "Knock what?")
  return
end

if obj == pl then
  send(pl, "You can't knock yourself.")
  return
end

if getflag(obj, flag.CanOpen) and state(obj)==0 then
  if getflag(obj, flag.Plural) then
    send(pl, "They're open.")
  else
    send(pl, "It's open.")
  end
  return
end

act(pl, "%#1 %[knocks/knock] %a.", obj)

local other = getobj(obj, "other")
if other then
  act(other, "%#1 %[is/are] knocked from the other side.")
end