According to all the commentary I can find, mob heads should be attachable to picks to add a level of mining XP or mining effectiveness (it's not clear which).

However, using either your personal crafting grid, the crafting table, the tinkers crafting table, or the tool workbench, I can't attach a mob head (Treating it as either a repair part or a modifier). Nothing happens, no new item is available, everything just sits on the grid.

I'm using 1.7.10, Resonant Rise 3 latest package (118 mods loaded...), Forge 1401

EDIT:
My main.cfg says the following, so it should be enabled.

pickleveling {
# Mob heads can be used to boost a pickaxe's mining xp. [default: true]
B:addMobHeadBoost=true

# Mob head boosting requires a free modifier [default: false]
B:mobHeadBoostNeedsModifier=false

My pick is a fully repaired, bone-handled, wood-bound copper pick. I have upgraded it repeatedly after building it, but it won't mine anything above copper ore.
I have tried zombie, creeper, and skeleton heads.
I have two free modifier slots.

It's using the default harvestlevel progression for IguanaTweaksTConstruct - wood flint copper iron etc.

Does RR3 use the changed harvestlevel progression? It works fine for me otherwise, no modifier needed.

Resonant Rise isn't the issue!
tested IGUANATINKERTWEAKS-1.7.10-2.1.5.jar
I spent an hour testing:
I had something similar happen to me. Thought it was because of KCauldron, but it wasn't. Extra TiC from Extra Utilities is the culprit from the TCon Integration thing. Given your mod adds function I'd assume it would be fixed on your end and not Extra Util's end, should we forward this issue to them 2?

the all flint tool can get the mob head
The tool with Extra TiC parts doesn't even have an Mining XP Bar, yet I'm Skill : Master

Now see that this item has Extra TiC binding and tool rod

should change title to : Extra TiC Mining Level Compat

possibly related to #144

You're right, it had a magical wood binding!

I've changed the name.