Sense 2 objects touching

I have been wondering how to do this for a while but I can not seem to find a good solution. I could use a good solution in multiple projects.

I have 2 objects, both objects are costumizable in the way that I prefer. I want to sense if the 2 objects are touching (rapid touching). I have been thinking about IR, magnetic fields etc but I need to be sure that they are actually touching (close proximity is not enough). Providing both objects with a metal piece that connects seems to make sense but as my as my knowledge reaches I always need a 2 channel connection to send signal between object 1 and 2. I can not have a two channel connection, only one is possible. Is there a way I can let object 1 know when object 2 is touching using only one contact point? I have been thinking in the direction of small sparks causing a small ??voltage drop?? but don't get far there. Anyone any ideas?

Ground the metal contact point on one of the objects, and connect the metal contact point on the other to a digital input pin. Enable the pullup resistor on the input pin. The pin will read LOW when they are touching, and HIGH when they are not.

Of course, anything else that grounds the second object's contact point will also register.

In case both objects are teddybears, their noses are metal and I want to know when they touch, how do I ground the contact point? My electronics knowledge is really basic.