Awkwardness grows when everyone begins performing how little they noticed it.

An awkward moment is usually small until people start managing it. Somebody stumbles, and then three people become very casual, talk slightly too brightly, and work visibly hard at having noticed nothing. The performance is louder than the original moment, and everybody can tell it is happening, which is what turns a half-second into an atmosphere. The effort to smooth it is what makes it rough.

When something clumsy happens, let it be ordinary rather than covering it. A short acknowledgement, or simply carrying on at the same pace, ends it faster than any amount of tactful behaviour.