Attachment ID and util.SpriteTrail

I want to attach a sprite trail to this bone ValveBiped.Bip01_Pelvis. How would I convert it into a number? Assuming you have to o.0

[lua]local boneind = pl:GetBone(“ValveBiped.Bip01_Pelvis”)
local pos , ang = pl:GetBonePosition(bondind)[/lua]

**[Entity.LookupBone

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