.htaccess rewrite will accept a number but not a word

I’ve got a really strange problem that I can’t find the answer to.

I’ve got the following redirect rule set up

RewriteRule dog-parks/dog_park/([^/]*) /index?pagename=dog-parks/dog_park&title=$1 [L]

It works when I put a number after dog-parks/dog_park/ as in dog-parks/dog_park/12/ but when I put a word instead like dog-parks/dog_park/word, it’s not recognised and the query params does not come through.

Any idea why? Please help.

PS: I’m using WordPress (if that helps anyone)