Literally: Putting in one’s grain of salt.
Meaning: To add one's two cents; Put in your tuppence worth.
To designate an intervention in a conversation or situation with an unsolicited comment or opinion. Depending on the context, a person’s urge to slip in his grain of salt can be seen in a positive light (outspoken/endearing) or a negative one.
Origins: 20th century, comes from Latin “Cum grano salis” meaning taking something “with a grain of salt.”