The regular past tense in English is formed by adding "ed" to the verb. This past tense regular verb ending has three distinct sounds ("t", "d", and "id"). Captur is an ideal way for teachers to find out how well their students understand these sounds.
When we use Captur paddles for pronunciation activities, we are mainly looking at whether or not our students can distinguish between certain sounds, either receptively (listening) or productively (speaking).
It's usually pretty difficult for my Japanese students to make the distinction between "thirteen" and "thirty", even at the lower intermediate level. Often, when they say a number like 16, it sounds like "sixty", and when you repeat the number in English to confirm it ("Did you say sixty?"), they say "yes, 16." This page talks about using Captur Paddles with words that sound similar.