It's a mark on his neck. You scratched your neck and got the same thing. Why are you still worrying about this?
If the mark appears again then once you're close to him just say 'oh hey whats that mark on your neck?' as if you just noticed it. But really, if you're jumping to these sorts of conclusions over a tiny mark (if it was anything else, wouldnt he have tried to hide it??) then perhaps you need to work on the whole trust issue.
"When I was 4 years old, they tried to test my IQ.
They showed me this picture of 3 oranges and a
pear. They asked me which one was different and
did not belong. They taught me different was
wrong."
- Ani DiFranco -