Why do they use wood instead of bells?

During Mass tonight when changing the bread and water into the body and blood, they knocked wood together 3X instead of bells? Why is this?
Thank you

According to liturgical rubrics there are no bells between the Gloria on Holy Thursday and the Gloria at the Easter Vigil.
Bells are associated with celebratory imagery. The spiritual journey of the Holy Thursday Mass is to place us in the context of the night Jesus was betrayed and handed over to death. Anything considered overly joyful or celebratory is avoided, even organ use is limited to only accompany singing.
In celebrating the Sacred Triduum we strive to not simply “recall in our mind” the events of Holy Week but rather in a spiritual manner place ourselves in their very midst. The use of the clapper instead of the bells is a reminder of the solemn nature of the liturgy. Some have claimed that the clapper also serves as a more strident reminder of the sacrificial nature of the Eucharist since its noise resembles something being hammered.

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