Introduction. Capnography is an essential part and standard monitoring tool during the perioperative period, which can be invaluable in detecting anaesthetic equipment malfunction. Case report. The atypical, ’’tails- up’’ capnographic waveform was noticed during routine surgical operation. Comprehensive physico- mathematical and graphical explanation of this complex capnographic pattern has been given, together with in- depth analysis of possible differential diagnosis and clinical significance for routine clinical practice. Conclusion. “Tails-up’’ capnographic trace gives early clue to diagnosing and fixing the problem of cracks in sampling line, before leading to an inadequate course of action. The understanding of the physics and physiology behind capnography is of vital importance for the analysis of capnographic waveforms, for early detection of anaesthetic equipment malfunction and for safe clinical practice.