Simplifications: processing of goods: processing by different suppliers in the same Member State
The Principal (A) in Member State 1 (MS1) sends goods to Member State 2 (MS2) to a processor (B). But rather than being returned to A they are passed to a further processor in MS2 (C). The finished goods are then returned by C to A in MS1.
B and C are supplying processing services to A who will account for the VAT due on each supply as a reverse-charge. The movements of goods between the Member States (which would otherwise amount to transfers of own goods by A) are disregarded as supplies and acquisitions.