diff --git a/constants.lua b/constants.lua
new file mode 100644
index 0000000..5e399c3
--- /dev/null
+++ b/constants.lua
@@ -0,0 +1,45 @@
+-- unavoidable table lookups used by multiple files are stored here.
+-- nothing in here should
+-- be changed at runtime.
+--
+-- also has commented "fake constants" that are replaced by actual values, for
+-- reference.
+--
+-- see index_map.md for more "constant" values
+
+function init_constants()
+   -- block_size = 64
+   -- biome_size = 128
+
+   -- the indices here are sprite numbers.
+   object_interaction_map = {
+      -- tree
+      [4] = {
+         replacement = 14,
+         sfx = 11,
+         drop = 65
+      },
+
+      -- big mushroom
+      [8] = {
+         replacement = 16,
+         sfx = 12,
+         drop = 66
+      },
+
+      -- cactus w/ flower
+      [10] = {
+         replacement = 15,
+         sfx = 12,
+         drop = 68
+      },
+
+      -- cactus
+      [13] = {
+         replacement = 15,
+         sfx = 12,
+         drop = 67
+      }
+   }
+
+end
diff --git a/index_map.md b/index_map.md
index da118b2..22a8fda 100644
--- a/index_map.md
+++ b/index_map.md
@@ -22,6 +22,7 @@
 65 - wood
 66 - mushroom
 67 - cactus meat
+68 - cactus flower
 
 ### sfx
 ---
diff --git a/infimap.p8 b/infimap.p8
index 640ff75..7a2fcc0 100644
--- a/infimap.p8
+++ b/infimap.p8
@@ -1,6 +1,7 @@
 pico-8 cartridge // http://www.pico-8.com
 version 18
 __lua__
+#include constants.lua
 #include sound.lua
 #include mapgen.lua
 #include player.lua
diff --git a/main.lua b/main.lua
index c746a82..bf80e43 100644
--- a/main.lua
+++ b/main.lua
@@ -1,4 +1,5 @@
 function _init()
+   init_constants()
    init_sound()
    init_mapgen()
    init_player(32, 32)
diff --git a/mapgen.lua b/mapgen.lua
index 40c6fa8..f04f8fb 100644
--- a/mapgen.lua
+++ b/mapgen.lua
@@ -2,8 +2,6 @@
 
 function init_mapgen()
    uid_seed = 2229 -- arbitrarily chosen number
-   -- block_size = 64
-   -- biome_size = 128
 
    -- Metadata for different biomes
    -- frequencies don't have to add up to 100, but they should by convention
@@ -36,7 +34,7 @@ function init_mapgen()
       local biome = biome_list[i]
 
       -- add the biome's name N times to the biome metadata 'hat'
-      for i=1,biome_data[biome]["biome_frequency"] do
+      for i=1,biome_data[biome].biome_frequency do
          add(biome_metadata, biome)
       end
 
@@ -47,7 +45,7 @@ end
 -- build the lookup table for a given biome, based on the biome_meta data for
 -- that string.
 function build_biome(biome_name, data)
-   local meta_frequencies = data["tile_frequencies"]
+   local meta_frequencies = data.tile_frequencies
    local tile_lookup = {}
 
    for i=1,#meta_frequencies do
@@ -57,7 +55,7 @@ function build_biome(biome_name, data)
       end
    end
 
-   data["tile_lookup"] = tile_lookup
+   data.tile_lookup = tile_lookup
 end
 
 -- generates a unique identifier for a position
@@ -90,7 +88,7 @@ function get_tile(pos_x, pos_y)
    local biome = biome_data[biome_name]
    local uid = generate_uid(pos_x, pos_y)
 
-   return biome["tile_lookup"][(uid % #biome["tile_lookup"]) + 1]
+   return biome.tile_lookup[(uid % #biome.tile_lookup) + 1]
 end
 
 -- generate the map and writes to the map area from 0 - block_size,