Colliding with an undetected creature?

[hyphz]

What happens if a moving creature collides with an undetected creature? I could not see anything on this in the Stealth or Movement rules.

The "common sense" option is that this detects the creature and makes it Hidden, but this seems a risky approach, since it potentially makes just moving around more effective than the Seek action. A character with a 25' speed can cover 15 squares in a turn - equivalent to a 20' burst area including the square they started in - and presumably a collision would not require a roll against the target's Stealth DC, meaning that it provides certain information.

[Edge93]

I think it would be reasonable to assume that the invisible creature could allow the other creature to pass through without revealing that. It's entirely feasible to walk through the same 5 ft. square as someone and not run into them.

[hyphz]

Another question that came up was what happens if a ranged attack is aimed through the square of an invisible and undetected creature. Absolutely RAW this just gives screening / minor cover but that doesn't make a whole lot of sense.

[Castilliano]

The invisible person can let someone pass through their square, just like an ally can. They can also choose to resist that, though that signals where they are.
The trouble is when a person wants to or has to stop on the invisible person's square.

The invisible person gives cover like any other body.
It doesn't stop vision, but it does stop arrows (assuming a normal physiology!). If the attack misses by the cover bonus, I might give witnesses a Perc roll to see where the arrow was deflected.

Cheers