the motor supply circuit by entrainment of the cam in the rest position 126 of the lever shown in solid line the electrical circuit of the motor is closed and the motor starts up as soon as the power cord of the appliance is connected the blade 127 is lowered into the compartment 128 to freeze the preparation when the blade is withdrawn under the increasing force generated by the freezing of the preparation the projection 129 comes into contact with the lever 126 as the arm 131 rotates and causes it to pivot into the position 130 shown in broken line this rotation results in breaking of the motor supply circuit and activation of the alarm if any under the action of the aforementioned cam when the appliance is used again it is sufficient to grip the lever by hand to return it to its initial position 126 in order to be certain that the two or more blades have been withdrawn when the motor is stopped it is necessary for the other blade to be withdrawn before the blade equipped with the projection 129 to this end springs opposing the force attributable to mixing and accommodated in the hubs of the blades are shown in fig1 and 11 as provided in application ser no 292 121 of sept 25 1972 now u s pat no 3 916 637 fig1 and 11 correspond to fig4 and 5 of the patent with the addition of projection 129 thereto arm 131 may comprise at each end thereof two aligned forks 14 and 15 as shown in fig1 the fork 15 receives a nut set into plastic and on.