Box2d - get indices of new object contacts

Hi guys, I got a little bit stuck here while playing around with box2d physics.

I want to get the indices of new slices in the getcontactdetails node, to do impact animations. Checking the spread for changing values won’t work, since I just want to animate on creation.

isnew just outputs a spread of zeros with the according slicecount, so it seems quite useless.

Tried to do comparisons with select and intersect, but did not get my mind around it. any help appreciated. :)