I noticed something about my wife from the minute we held hands - she tucked her thumb inside so I ended up holding her hand - engulfing it, I suppose. I couldn't figure it out because I learned growing up in the rough neighbourhood where we lived never to tuck your thumb inside your fist because you never knew when you'd have to punch somebody...yeah, sad but true. On the good side, she doesn't punch me :)
Punching someone with your thumb inside could result in it being broken! That is strange about your Wife ?,perhaps clasping Taxi money in case she needed to get away?
Ha ha, that might explain a lot :)