Fig. 2. Pneumotach mask construction. (A) A small amount of clay (cl) is placed over the turtle's nares. (B) Dental impression material is applied over the clay and face (avoiding lower jaw; turtle breathes through the mouth during this phase). The mask is then removed and trimmed and the breathing port (bp) is inserted. (C) Clay is placed over the mouth, dental impression material is reapplied (over the mouth but not the nares; turtle breathes through the nares during this phase) and the previous mask is pressed into place. Once the composite mask has cured and been trimmed, it is attached with surgical adhesive on the day of the experiment and the pneumotach (pn) is inserted into the breathing port.