I also say gesundheit and sometimes I say "That's funny."
I use gesundheit too.
I've never understood the "bless you" when one sneezes. I find unrequited blessings wrong.
People used to think that when you sneezed, your soul left your body. With your soull missing, the devil could enter your body in place of your soul. In order to prevent that from happening, people would say "bless you" so that God would get in before the devil could.