
In an undertone
Discreet Conversation
Use 'in an undertone' when characters need to speak without being overheard, indicating secrecy or privacy. 
Expressing Disapproval
'In an undertone' may convey a speaker's disapproval or sarcasm about the discussed subject. 
Emotional Restraint
Characters might speak 'in an undertone' to hide strong emotions like anger or excitement. 