4th step - classifying collisions - number of neutral particles from collisions

Neutral particles do NOT leave trails of bubbles (because bubble formation is initiated by the ionisation of the hydrogen atoms by the Coulomb interaction). However, occasionally an unstable neutral particle can decay in the bubble chamber into a pair of particles - one positive and one negative - leaving an easily recognisable letter vee shape (move cursor over the picture).

If the vee tracks happen to cross again, downstream the line joining the crossing position to the decay position points back to the origin of the neutral particle.

So our Vee can be seen to be coming from the collision and not from the kink.