One day Yao-shan Wei-yen (750-834), one of the well-known Chinese Ch'an master, was asked by the host of the monastery to give his sermon to the assembly who for a long while was expecting his teaching. Yao-shan said: "Strike the bell."
Just sharing , sorry in advance . In human culture of all races ...saying "thank you" is a gesture of respect , polilteness and is accepted as a great action .........But in my current understanding of Buddhism , one need to say it all moment of his life , each moment as he lives because all beings is providing him knowledge , understanding , factor of realization , experiences to un-cover , discover himself ........so not limited to any special action but is a emotion .
In Buddhism one will feel the need , without anger even to the killer of his love one because he provided a chance to discover his emotions towards his love love and the killer .............all beings regardless their action is providing us a lesson to discover ourselves and being a teacher to us ................................thank you . BUT in my current condition with full of emotion / polluted energy , I will certainly kill the killer of my love one ...I still need to learn , thank you for teaching me.