       @genes.maxAcceleration[0] = @genes.maxAcceleration[0]()
     else
       @genes.maxAcceleration[0]
-  maxSpeed: -> @maxSp ||= @radius * 1.5
+  maxSpeed: -> @maxSp ?= @radius * 1.5
   react: ->
     super()
     x = 0

    names = {}
    @visitThings(
      (t) ->
        n = names[t.type] ||= t.typeName()
        counts[n] ||= 0
        counts[n] += 1
      false, true
    )

class Stone extends Thing
  constructor: ( location, options = {} ) ->
    super location, options
    @bodyColor ?= 'grey'
    @radius = options.radius || 8
    @type = Stone
  drag: -> 0
