Thepersonisclearlyfeelinganxiousandistryingtocalmthemselvesdown a clenchedjawspeaksofthesameconversationisdefinitelygoinginanunpleasantdirectionforyourpartner.
If a personisgivingyou a glovehandshaketakingyourwristintherefreehand, they'reshowingthattheyaretrustworthy.
Thissomeoneisputtingtheirpalmonthetopofyourhand.
They'reshowingyousympathy.
That's iftheydoitinstantly, though.
Ifyou'vebeenshakinghandsfor a whileandthentheydecidetoputtheirhandontop, it's a wayofshowingwho's theboss.
Holdingsomeone's handfrombelowisliketellingthemyou'realwaysthereforthemincase a personisinvadingyourprivatespaceandcasuallytouchingyourelbow, forearmorotherbodypartduringthehandshakewith a freehand.