We bought more teasers over the weekend, specifically a replacement feather teaser and a pom-pom teaser. Both passed.
An interesting use for two teasers is that when Billy the Mighty Hunter pounces on one teaser, the second teaser can be used to retrieve the first teaser. Basically, he doesn't know his own limits -- he can't keep two prey trapped at once, but tries anyway.
Unfortunately, Billy still seems too agressive with the teasers; I am cutting him off. He will still get to attack the ribbon teaser, which he doesn't seem too violent with.