In John 6:41, the Jews grumble because of Jesus' claim — this is the specific grumbling Jesus rebukes in v43.

In John 6:64, Jesus reveals he knows which disciples disbelieve — linking his rebuke of grumbling to their underlying unbelief.

In John 16:19, Jesus perceives the disciples' unspoken questions — another instance of his divine knowledge of hearts, as here he knew their grumbling.

In Matthew 16:8, Jesus similarly rebukes disciples for discussing among themselves about bread — echoing his awareness of their grumbling here.

In Mark 9:33, Jesus confronts the disciples' argument about greatness — another instance of him addressing their internal disputes.