When Houdini was tiny (rescued him from the pet store dog food display at two days old) he would have trouble with even chopped nightcrawlers because they were a bit sticky. If he got a chunk even a little too big, he would kind of choke and end up having to wipe it out of his mouth on the side of the water dish. It's probably just the size and the fact that checkereds aren't as crazy about slugs as NWs.

But better safe than sorry! We have a tree trunk that always has literally HANDFULS of good slugs in it, but nightcrawlers are so cheap and I'm so paranoid I've never bothered