Final answer:
The subject of this question is Mathematics, specifically the use of congruence in a 'magic trick'.
Step-by-step explanation:
The subject of this question is Mathematics because the question is asking about the use of congruence in a 'magic trick'. In mathematics, congruence refers to the concept of two figures having the same shape and size.
It is often used in geometry to compare and analyze shapes. In the context of the magic trick mentioned, it is likely that the sphere used congruence to create an illusion or trick involving shapes.