The basics of functioning and tuning of wind instruments is reasonably explained by small-amplitude descriptions. Some details must be cleared up, such as corrections at the hole/bore transition, bends, and radiation at hole ends. In some cases, however, the linear description fails. For example, a clarinet becomes unplayable when its usual holes are replaced by much smaller and shorter ones (of the same impedance) [D. H. Keefe, J. Acoust. Soc. Am. 73, 1804--1820 (1983)]. Since it was noted that this tube could be blown with another (i.e., a saxophone) mouthpiece, it was supposed that the superimposed static flow influences the tube impedance. This assumption was provisionally confirmed by measurements. Understanding this phenomenon may help to improve the ease of playing of the lowest notes on saxophones. The common quantitative description of the flute action does not explain why certain fork fingerings cannot be blown and why the ``reed-flute'' has a dominating fifth harmonic in its initial transient. To contribute to the discussion on the influence of wall vibrations on tone quality, a mechanism will be proposed which is possibly responsible for a coupling between air and wall vibrations.