(A) This and the next four panels depict matrices of similarity between mFRFs in pairwise (row against column) combinations. This first matrix illustrates similarities before dye application. (B) Matrix comparing the dyed and undyed conditions. (C) Matrix comparing whiskers after dye application. (D) Matrix computed for FEM-simulated (Sim) whiskers. (E) Matrix comparing one whisker over time. Time measures begin with ‘cut’ (immediately after whisker extraction from the snout), ‘dye’ (immediately after dye application) and ‘pol’ (immediately after the application and drying of nail polish). (F) In the upper panel, the diagonal values of the matrix shown in (B) are plotted (each whisker against itself, before and after dyeing). The set of values obtained by taking the i-th sub- and super-diagonal values of the matrix shown in (B) are averaged and represented with horizontal lines labeled i. The further from the main diagonal, the smaller is i, indicating that mFRF similarity decreases with increasing disparity in whisker length. The values of the diagonal are always high, highlighting the absence of dye effect on all samples: despite the application of the dye, each whisker is always more similar to itself rather than to other whiskers. On the lower panel, the supra-diagonal values of the comparison matrix shown in (E), which highlights stability up to the application of polish. In particular, by reference to the horizontal lines shown in the upper panel of (F), the change of the whisker caused by polish can be compared to the difference between the two whiskers of length 18 mm and 56 mm.