Simple Q&A D&D 3.5 (by RAW) XX

[sonofzeal]

Q59

Dire Weasel is attached to a spellcaster. What kind of implications does attachment have if the caster tries to cast a spell? What sort of concentration check (if any) is required?

A59
Indeterminate. RAI almost certainly considers it a grapple, but RAW doesn't quite say that - meaning no penalty. Your DM is well within their rights to treat it like a grapple though.