Strong and prolonged eye contact. Finger touching every time an object is exchanged when there are definite and easy ways to avoid contact. Being guided by a hand on the back or by the arm. Personal questions (do you have a boyfriend?). Possibly subtle teasing (not sure).

Flirting or normal behavior? I guess it could go either way. Definitely some people just make good eye contact and ask questions to get to know a person. The other two seem a little in the gray area… But from a married professor with kids? Although there is not much age difference.

In any case, I think we at least have great chemistry as colleagues and could possibly see us being good (platonic!) friends.