avatars won't show in comments

The avatars in comments won’t show. Not even the default gravatar dude displays. Instead it’s just an empty box. Avatars display everywhere else, just not in the comments.

Based on the searching I’ve done, it looks like my problem should be in Comments.php or Single.php, except my theme doesn’t have a Single.php.

Can anyone tell me where to start? Here is an example of the problem I’m having.