Click and drag the vertices of the triangles around. Notice the difference between how ABC behaves vs. DEF:
Some questions to consider:
What were the different effects of moving the vertices of ABC?[br]What about DEF?[br][br]What could you do to ABC to change it to a non-congruent triangle?[br]What about DEF?[br][br]What do the differences between ABC and DEF tell you about SAS?