I tried swapping it out with what you wrote. And it does the same thing. "Lion" works but "Tiger" doesn't. It's always the 2nd one that doesn't work.
%count = $regex($1-,/(?:^|\s)(?:Lion|Tiger)\b/g)
Edit: I think I found out where the actual problem is:
on $*:TEXT:/Tiger|Lion/:#:
What's wrong there?