u/AnnualImplement5829

1. They have the same first 2 initials in the name "HJ"

2. Apparently both their mothers' maiden names start with an "E" and commonly boy names: Evans and Elliot.

3. They can use each other's wands with no problem.

4. Both are known to have wild messy hair.

Heck, she at some point in the development of the story was planning for Potters and Grangers to know each other beforehand, which really points to them being more like soulmates.