«يَجْعَلُونَ أَصَابِعَهُمْ فِي آذَانِهِمْ»
They put their fingers into their ears—meaning the tips of their fingers.
In Qur'an 2:19 the term «أَصَابِع» names whole fingers, while the parts inserted into the ears are the fingertips. This is whole-for-part (kulliyya).
The expression also intensifies the imagined effort to shut out a disturbing sound. The rhetorical vividness accompanies, rather than replaces, the logical classification.