If only a foot, hand, tail or other part of body is visible on the post (e.g., disembodied) - it can be the main focus of the post - and the character is mentioned by author in the description, is it enough to tag the character? If the tag was added by the artist, should it be kept or removed? Especially if this body part has a lot in common with others (a regular white paw, a brown furry digitigrade foot, red fox tail, etc.) and you can not recognize the character without additional context (description, story in comics).
TWYS says, that "E621's tagging system is intended to relay virtually NO ADDITIONAL INFORMATION or context about an image," and "all tags on a post are only claims as to what's visible in an image, not what "actually is" in an image".
For example, post #3403160 has multiple paws, but it is very unlikely to recognize characters without looking at their other works (character tags were added by community). Post #3130431 has single foot, and the artist claims that it's Candide's (the character tag was added by the artist), but it is hardly recognizable without any context.