MasterM, Chip off the Old Block

MrsM finds the following letter

Dear MrM and MrsM

Unfortunately on Wednesday MasterM was involved in an incident where he made plastic pellets in the Design Technology lesson which are capable of being fired by a rubber band. The situation has been dealt with within school but there may still be a number of pellets at home, and if so, could you please ensure that MasterM returns them to me.

Yours sincerely
Hapless Design Technology Teacher

MrsM had forgotten about this 'incident' and shows the letter to MrM who blushes.

MrM
"I may not have mentioned this at the time but when I was the same age as MasterM the Art teacher left us unsupervised for a while. My friend, who was a farmer's son, suggested that we make clay pigeons and we set to diligently. We probably would have got away with it but then we decided to test the clay pigeons by throwing them at the wall. By the time the teacher returned there was wet grey clay everywhere so we had to spend the rest of the lesson washing the wall."

MrsM looks suitably shocked.